The one in it uses one power cord I believe. You are saying that the 5870 uses two? If so, how many does the computer have?
Yes, the 5870 would use two. If the x1900 uses a
6-pin PCIe power connector, then you can re-use its cable for whatever video card(s) you use to upgrade.
Will I be able to run this and the x1900 without stealing the second optical drive?
http://milwaukee.craigslist.org/sys/2815287196.html
It'll also save around $400 compared to a 5870.
That will probably run. If you browse the forums, you'll see that a lot of people (myself included) generally have luck with XFX cards. This is not the exact card I used, but it should be very similar. You should be able to find 5870s for less than $475. The Apple-specific card is that much, maybe, but PC components are not.
And if I understand your question about the 2nd optical drive correctly, then yes: if you simply swap a 5770 in in place of the x1900, you will not need to purchase or install any new cables.
If you need three auxiliary feeds, you'll have to either branch off of an unused Molex power connector (like the one for the lower optical drive bay, assuming nothing's installed there) with an adapter or run a secondary PSU. Several companies make small PSUs that fit in an optical drive bay.
However...
Unless you plan on running more than two displays, there's very little point in keeping the old X1900XT in your machine after you upgrade.
This. Once you start seriously adding more hardware that requires more power (like additional video cards), you're going to have a much more serious project on your hands. Very doable, but a hassle. And I HATE dealing with PSUs, so adding additional units are generally something I try and avoid.
My understanding breaks down a bit here. I think both the 5770s and 5870 will support three displays under Mac OSX using dual-link DVI (if I'm wrong, someone please correct me). If I am indeed wrong, and you require a second low-power card for your third monitor, might I suggest finding an original Apple 7300GT? It's a god awful card to use as your primary GPU, but for simply running an extra display, it should do nicely. It also has no additional power requirements other than the PCI slot:
http://www.ebay.com/sch/i.html?_fro...3&_nkw=apple+7300gt&_sacat=See-All-Categories.