My poor old laptop won't run 7; it has a hard enough time keeping up with XP. And it's behind a careful firewall at my router - well, except when I travel.
My desktop runs 7 and I love it, but it's a much newer machine.
So you're taking a risk -- you should just recognize that and admit to it. I'm not sure why you're qualifying. I may have a laptop from 1997 that can only run Windows 98 comfortably but that doesn't make it secure or a good choice for security in 2010. Sometimes you just have to spend money and upgrade.
By the way, a newish 2.6 Linux kernel with WINE should do most of what you want and approximately the same system requirements. Your mileage may vary if you have an obscure Windows-only program.
I do, in fact, have more than one obscure Windows-only program - the entire translation industry is Windows-only.
I'm not sure why you think I "have" to spend money and upgrade. I can't lose data, and I don't keep sensitive data on a laptop - the worst that can happen is that I have to reinstall the machine if it's beyond rescue.
My desktop runs 7 and I love it, but it's a much newer machine.