Im gonna get a Windows Vista Ultimate from ebay 170 bucks I think dont feel like checking anyway hows the speed on a imac, how much space does the vista OS its self take up i heard premium takes up like 25 gigs.
I've got Vista Ultimate on my machine, and it's taking up 38 GB of Space right now. But, I've also got lots of small Quicktime movies taken with my digital camera, lots of still pictures of the kids, several different photo editing programs, and my Antivirus program, a Windows 2003 Virtual machine with Virtual PC, several utility programs, an SQL server, and lots of other stuff.
About 10 GB of Space (just checked) is just the miscellaneous pictures and project files stored on my desktop. So, that would mean that only 28 GB of space is being occupied by Windows, my various projects, my Virtual PC with Windows Server 2003, and other misc. stuff.
I've heard of people installing Vista in partitions as small as 10 GB.
I've set up a 100 GB partition on my machine just for room to grow. But, if you weren't planning on much, I'd probably be comfortable with a 50 GB partition.
I like to have lots of room to grow just in-case my needs change in the future. A 100 GB partition for Windows is plenty for me. Now, my OS X environment takes nearly a terabyte, but that's different ;-) I have a ton of stuff in OS X (lots of video projects in various stages).
As for speed on the iMac, I can't really give you a direct comparison. And, it would depend on the specific iMac anyway. But, the comparison I can give you is from my machine to my wife's machine:
My Machine: Mac Pro 2.66 GHz Quad Core. 14 GB of RAM, 100 GB of drive space for Windows, Western Digital Hard Drives (several) about a terabyte of space total (though dedicated to Mac partitions - only 100 GB assigned to Windows). Stock nVidia GeForce 7300 GT with 256 MB of video RAM, and dual 19-inch wide-screen LCD screen (each displaying at 1440 x 900 at 60 hz).
My Wife's machine: HP Pavilion d5000t with a 2.83 GHz Core2Quad (Quad Core), 3 GB of RAM, Hitachi Hard Drive (7200 RPM) 750 GB of hard drive space dedicated to Windows, nVIDIA GeForce 9800GT w/ 1 GB of Video RAM, dual 22-inch wide-screen LCD monitors (each displaying at 1680 x 1050 at 59 Hz).
And, for comparison purposes (using the built-in performance rating system in Windows), the scores on her machine compared to mine are:
Her system, all 5.9 (the highest score possible, so it might actually be higher if the scores would go higher).
My system:
Processor 5.9
Memory 5.9
Graphics 4.3
Gaming Graphics 5.8
Hard Drive 5.8
So, I guess the question is to compare your iMac's performance / specifications to my machine, and kind of estimate what you might see.
I can tell you that from experience, the Mac Pro does seem to be a bit slow booting Windows Vista, and is nearly as slow when shutting it down. Starting up is about a 3 minute wait. Shutting down is about a 1 to 2 minute wait. That's when running Windows directly and not in a virtual environment.
On my wife's system, I can have the machine up and running (from being off) in about 20 seconds. And, it will shut down about as fast.
When using the machines, her machine does feel smoother than mine, but the difference in performance is pretty minimal for most tasks. I would say you could only measure the productivity difference with a benchmark program.
One further note on hard drive space...
I just checked my wife's system, and her system is using 83 GB of hard drive space right now.
But, that 83 GB is holding:
Windows Vista Business 32-BIT
Microsoft Office Ultimate 2007 (full install)
Microsoft Office Accounting Express 2007 (Full Install)
Quicken Deluxe 2009
Various documents and pictures and other stuff
e-mails with attachments (some sizable) that go back to 2006 or earlier
McAfee Antivirus / Firewall (same as the one on my system)
Norton Ghost 14 (for disk imaging backups - works great)
and some other misc. stuff.
I'd guess that the majority of space is office and perhaps the e-mail attachments.
So, that will give you a few numbers to compare. I would seem to have a lot more on my system than she does, but mine uses less space.
I used to have Office Ultimate 2007 and the Business Accounting package on my system, and if I remember right, I think it brought my system up to around 60 GB of used space (though I cannot remember for sure).
Anyway, perhaps this will be useful in your assessment, maybe not. But, at least it's a start with some numbers.
Note when comparing my system to hers that I am using Vista Ultimate 32-BIT and she is using Vista Business 32-BIT. Both have all options installed and all the current software updates. Both are running the same Anti-Virus / Firewall. Mine is a Mac Pro, her's is a HP.
I would say that with the exception of startup and shutdown times, that I am pleased with Windows Vista's performance on my Mac Pro. In some tasks, it is actually faster than performing the same task in OS X (notably when accessing the Internet - browsing sites and downloading files).
Additionally, Windows will find wireless networks that OS X cannot (using the same hardware). A nearby network (around a quarter or half mile or so away (nearby for me) cannot be seen at all by any computer in the house running OS X. But, it can be seen by several in the house that are running Windows Vista or XP (including the Mac's which can see the network in Windows but not in OS X).
One other note, I (and many others) have had issues getting the built-in sound card and default speakers or default speaker jack) to work on their Macs when running Windows directly. My issue is still unresolved, some have gotten it to work, others haven't.
So, your speakers may or may not work in Windows (despite working fine in OS X).
I'm sure it's just an Apple / driver thing. Windows works just fine with the sound in my wife's system, and it uses the same chipset as my Mac Pro. I think it's just an internal wiring thing with Apple, and their customization not getting along with the drivers (including the ones that Apple supplied).
My sound works fine in OS X through my external speakers, but sound only comes through the internal speakers of my Mac Pro in Windows.
Anyway, hopefully you'll find some of those notes helpful in making up your mind of which way to go, or how you want to set up your machine.
If you have the hard drive space, I'd recommend a 100 GB partition for Windows. Anything you need beyond that could be handled by an external drive. If you're short on space, I'd probably recommend no smaller than 50 or 60 GB just so you don't run short real fast with other programs you may install. And, keep in mind that you'll want room for the swap file / virtual memory that Windows will set up as temporary storage (OS X does this as well).