Whenever possible and the computer is a 64-bit machine, you want to use the 64-Bit version of Vista, which is usually labeled "x64". The 64-Bit edition performs MUCH better than its 32-Bit sibling (labeled "x86"), and in my experience the difference is like day and night.
However, you might run into compatibility issues with your MacBook Pro. As far as I know, only the more recent Mac Pros come with 64-Bit Boot Camp drivers, while Apple provides all other computers only with 32-Bit drivers. This is a stupid policy, especially since the 64-Bit Boot Camp drivers for the Mac Pros also work with other Intel Macs that use a 64-Bit CPU (like your MacBook Pro, when it is a Core 2 Duo machine). There are torrents on the net for the 64-Bit Boot Camp drivers. Once you've installed the 64-Bit drivers, you can download the official Boot Camp 2.1 update directly from the Apple website.
And before you try it: The 32-Bit Boot Camp drivers won't do you any good on 64-Bit Vista.
Yes, this all is confusing and even more so because of Apple's inconsistent and customer-unfriendly support policy for Vista x64. It's just my wild guess, but this could be because Vista x64 beats the crap out of Leopard on the SAME Mac when you look at the performance. At least it does so on my Mac Pro. This, of course, is not good for Apple's marketing.
Anyway. If your MacBook Pro did not come with a 64-Bit compatible version of Boot Camp, download the 64-Bit version for the Mac Pros, it should work. How can you tell if your Boot Camp drivers are 64-Bit compatible? When you're in Windows and insert the Leopard DVD, you should find multiple installer files that carry "x64" in their name. But the most important file should be in the root directory of the DVD. If you don't have a Boot Camp x64 setup file, your Boot Camp drivers are NOT 64-Bit compatible.
Oh, and don't let anybody talk you into believing that it is "illegal" to download the 64-Bit drivers through a Torrent. It's unsupported at best. You own an Apple computer and a software license for that crap. And we're only talking about driver software here in the first place. Drivers that can mostly be downloaded all over the Internet from the various hardware vendors Apple is buying their parts from. For example, you will most probably want to download the graphics drivers rather from nVidia's website than use the ones coming from Apple, because nVidia's drivers are more recent and FASTER than the ones Apple gives you.