If it isn't broke, then don't fix it.
I have no problems w/Vista, my network consists of.
Windows SBS 2003 Server
2 Vista Business Edition Machines,
1 Vista Ultimate Tablet PC
2 IPAQ's
1 Linux Server
1 Linux Desktop
1 Windows 98SE Machine
4 Windows XP Machines
2 Windows Media Center Laptops
These are all tied into one network. My thoughts are, MS is good, but customers run out of money cuz of MS, so I try and save the customer money by alternative means.
I even have a customer running Windows 3.11 still !!!!
Windows won't ever expire.. but support will end for XP sometime in 2017.
If you do decide to run w/Vista then be heavy on the graphics card and run 2 gig of ram (you won't be sorry).