Microsoft has just announced that they will be providing for users of Window 7 Professional and Ultimate a really neat feature called "XP Mode"... This will allow you to run native Windows XP Service Pack 3 in a new "virtual machine" under Windows 7. So even if you do find some really old utility or game that won't run under Seven (which means it almost certainly wouldn't have run under Vista either) you can run it in XP Mode and you are all set. This is an additional download you can get from Microsoft after you install Windows 7. It even includes XP, so you don't need to have a copy or a license. If you own Seven you get XP for free for that installation.
http://community.winsupersite.com/blogs/paul/archive/2009/04/24/secret-no-more-revealing-virtual-windows-xp-for-windows-7.aspx