I use a previous gen Macbook Pro everyday as my main windows dev machine, but I run and recommend x64 XP Pro rather than Vista for the main reason that its not such a resource hog!
Its a 2.4Ghz Intel Core 2 Duo with 4GB RAM (OSX 10.5.5) with x64 XP Pro running on VMWare Fusion 2.0.
1.5GB RAM is allocated to XP, and 2.5GB to OSX. I run vs.net 2008, sql 2005, office 07 and expression tools, and use twin monitors. OSX is used for everything but development; mail, RDP, VPN connection into the office, itunes/iphone syncing. XP is purely used for development. I also use OSX for making music, using Ableton Live as it tends to be a lot more stable than on XP.
The trackpad is fine, and the keyboard shortcuts work great too., although Ive normally got an external keyboard & mouse plugged in.
Version 2.0 of VMWare Fusion is much more stable than 1.3, as I was often experiencing crashes while debugging in visual studio, normally related to memory corruption.
IMO, Get a MBP with 4GB runing VMWare Fusion with x64 XP Pro, and you'll enjoy the one of the fastest, most reliable windows development environments ever!