[Yawgm0th]

There won't be any traces left in the operating system, but it will be possible to tell that the program was there at some point so long as the hard drive is intact in its current form, though I don't think that's what you're after...

In any case, Steam isn't a piece of spyware as you think it is. Mind you, it can, under certain circumstances, prompt you to report certain information about your computer (hardware and software information, that's it), but it doesn't collect any personal information about you and report it to Valve. That said, I do hate it quite a bit. I think it's a terrible idea that has been implemented in a terrible way. However, it's somewhat of a necessity for online play, so I'll live with it.

As for getting Half-Life 2, you should note that you'll have to activate online, Steam or not.