the windows 7 beta is more or less fully functional and uses the same kernal as in vista so most programs that run in vista run in windows 7 as well
currently i have these programs installed and working without a hitch:
live messenger 2009
the only problem i have so far is the wallpaper slideshow features inability to handly any wallpapers larger than 1600x1200, not a big problem for most but most of my wallpapers are larger than that size ...
aside from that, windows 7 runs really well even on my 6 year old system (which used to have xp then became bogged down) with these specs :
p4 2ghz processor
512 mb ram
64mb video memory that came with the system