Unlike Vista which was built from scratch off the Server 2003 Kernel which has yet to get a vulnerability found for it.
Vista's kernel is 2k3's 64bit kernel with a few new features and kernel protection. 2k3's was based off 2000's its not from scratch.
The nt kernel dates back to 1988 (Remember os/2) its just been overhauled 9 times in total (5 times by microsoft )( *All 4 major os/2 releases featured a overhauled kernel* NT 3.1, Nt 3.5, Windows 2000, Server 2003 64bit/Xp X64, Vista)
Vista also features a new and exciting TCP/IP stack with more holes then swiss cheese. (Windows 2000 and XP used one based off the netbsd stack as all of microsofts attempts to make there own stack just resulted in them getting laughed at by script kiddies)
Also Vista's kernel "new" resource management was in XP X64's kernel.
Vista has the following selling points over previous windows releases
-30+ % lower performance when gaming with legacy graphics (Direct X 9 and older or open GL)
-Direct X 10 (Oh wow locking developers and gamers into vista)
- A new gui
-Additional Bloatware
If you want Vista without the crap (and sadly without Direct X 10) you want XP X64.