Will this game work with my PC?

I have a fairly old PC (it's only 2 years old, max, but what with Moore's law and all that, it was pretty much out of date as I queued at the cash register) so I'm concerned about buying games for it, especially as Game place so much frigging emphasis on you making sure it works for your PC.

What I'd like is a little app where I can plug in the game's required and recommended specs and it tells me whether it would run on my PC. All PC games seem to have these specs (ram, processor, etc) so it doesn't seem like a huge stretch to develop such a tool. I'm surprised nobody has come up with it already, and I'd write it myself if I had any experience of such a thing, but my googling has failed me so far.