Three Hard Drives, tripple booting

Nothing wrong with dual, or in your case, tripple booting. ...but its 2008, why not just virtualize? You could install the rock solid Vista 64 and use VMWare to install XP 32 and Ubunto in Virtual machines. Given enough RAM (6+GB) you could even run them simultaneously and network them together. Performance? You can assign each machine up to 2 processor cores so that it sees and can use two processor cores. You don't have 3D gaming performance in the virtual machines, however, so if that's what you really need then tripple booting would still the best solution to you.

...but VMware is so...elegant and powerful.

...and no, you can't disable 2GB of RAM in XP while the who enchilada is available to the other OS'. You've gotta find out why your XP 32-bit install is choking with 4GB in. Try this. Try totally turning off your page file, set it to 0. Don't worry, with 4GB (really 3+GB in 32-bit) XP won't miss the page file.

I'm not familiar with MokaFive, besides what I've just read, but if its anything like VMWare, you can do anything you'd do on a stand-alone PC besides using 3D hardware. You should be able to run Office, Access, and Visual Basic 6 with more than enough power, just like on a stand-alone PC.

Even if you're using a dual-core you should still find it very robust, I'd think. Heck, even Microsoft's own Virtual PC that can't give the guest OS use of multiple processors runs very well on a dual-core machine. Virtualization is really a powerful tool, often overlooked by many enthusiasts.