I agree with all the Parallels recommendations. Dual booting is a pain, and unless you want to play video games, performance in Parallels is good. You don't need to do any special partitioning - it runs in a disk image, which is just a big file. Here's a little blog entry that actually has a screenshot of Visio and Project running in Parallels.

I'd get the regular MacBook, kick it up to a gig or two of ram, and run parallels. I have the same VPN problem as you - Checkpoint don't make a VPN client that runs on OS 10.4.

Good luck - with the MacBook + Parallels, you really get the best of both worlds. Also, Parallels apparently employs the world's speediest programmers - it seems like they improve it every couple of weeks.