Need some game suggestions!

no more room in hell?

if you have a controller I'd suggest playing PSX games on ePSXe. It runs on a weak PC and there are gems (the FF games, vagrant story, Parasite Eve 1&2...)

Just suggesting because of the old pc restriction.

CS GO maybe?

Just Cause series.

Retro City Rampage, Bleed, Edna & Harvey: The Breakout, GTA San Andreas, Mutant Mudds Deluxe, Eldrich, VVVVVV, Knights of Pen and Paper +1 Edition, Cthulu Saves The World & Breath of Death. If you can run TF2, you can also probably run Portal 1&2 and Half-life 2. You might be able to run Fallout New Vegas on lower settings.

I was gonna sudgest Thief... But then I read a little further.

You should write what kind of games you like...

If you enjoy TF2 then perhaps older shooters would work - from what I've heard the older Call of Duty games are actually good, you could try CS:S or CS:GO, neither of which lag too much on a system that's vaguely similar to yours. Unreal Tournament might work. Stick with anything released before 2008 or built on Source and you'll be fine.

Or [spoiler]pirate it and see if it runs above 20fps before buying it[/spoiler]