I sympathize with you: ATI's Linux support definitely leaves much to be desired (I mean jeez - all they have to do is accept that "Open source" == "Open source", put a working code base out there ... and let the community do the rest!).
Anyway, even if you could get it to work (and I'm not at all sure you can), I don't think it would be practical. To be effective, your firewall really ought to be *external* to your host (or, at the very least, at the OS-level with your physical host).
IMHO .. PSM
There's another LQ thread where they're debating the usefulness of 32-bit vs 64-bit. As it sounds like you've already discovered, once you need >> 2 or 3GB RAM, you'll very definitely need a 64-bit OS. And until you hit that point, it's unlikely you'll ever notice the difference (difference in more RAM, and/or difference in 32 vs 64 bit OS).
A couple of years ago, I, too, had dual boot Linux/64 (SusE 10.0/64, specifically), and Windows XP/64. SuSE was absolutely no problem ... and Windows/XP was a fiasco. I wound up de-installing XP/64 and installing the standard XP/32, and I've been running happily ever since.
If Windows XP/64 happens to work for you - great! If not, I would run (not walk) to either Windows 7 (freely available in Beta) or Windows Server 2008 (which might be overkill - but which uses 64-bit very effectively).
Last edited by paulsm4; 03-07-2009 at 02:48 PM.