H.R.Shovenstuff said:
Thanks for the advice

I really am useless.
No worries. And it's not uselessness, you just don't know about the subject. (We can't know everything!)
Actually, you can answer your own question: I don't know if you are aware of this, but there is a recommended system settings for each game sold in Steam. Take Team Fortress 2, for instance. On the bottom of the page within the Steam client, you have the System Requirements:
Minimum: 1.7 GHz Processor, 512MB RAM, DirectX® 8 level Graphics Card, Windows® Vista/XP/2000, Mouse, Keyboard, Internet Connection
Recommended: Pentium 4 processor (3.0GHz, or better), 1GB RAM, DirectX® 9 level Graphics Card, Windows® Vista/XP/2000, Mouse, Keyboard, Internet Connection
You might want to clean out your hard drive though: if you're like me, you'll buy a couple of games in one go and it's startling how quickly your hard drive can fill up!