I must admit I have been a -NAY- sayer since Vista came out, but when I went to get this brand new laptop from Dell, then I ordered it with Vista and it runs like a dream, I won't even look back.
Yes it wont run with old "crap" just like most other computer technology, they are backward compatible to a certain degree. They can't keep sticking to old technology, they have to move on, update your programs and 10 year old printers and scanners and what not.
Most programs will run if you set compatability to WinXp sp2 and run as administrator (right click the program and change the settings).
The new Internet Explorer really explores the internet instead of just exploding which is quite nice.
If you plan on running Vista then get atleast 2 gigs of ram (2048 MB) with shared graphics memory that will be a bit less but still useable.
So by all means get Vista on a new machine, WinXP is dying. You might have to update some programs (if you do, you should have updated anyways even running on XP) and some old printers and such.