Is it possible to play two Steam games at once on the same computer/account?
I want to play Garry's Mod and Team Fortress 2 at the same time so when I get bored of one I can easily alt tab to the other and when I'm needed back on the RP sever I like to join I can go back then as well.
Steam doesn't have such limitation, but you can't play two games that use Source Engine at the same time.
Yes, you should be able to just alt-tab out of one game and open the other. This is a bit resource-intensive, though, so you may suffer some performance loss if you don't have a pretty powerful computer.