This is because most "Steam powered" games will ALWAYS install to where your STEAM client is installed. Now you basically got 2 choice.

1st, clear the harddisk of any other things to make space then install.
OR
Uninstall the whole Steam Client along with all other "Steam powered" games, then reinstall the Steam Client to your other hard disk partition to install mw2 to it.

Your Call. of duty..

EDIT: Might not be only 2 choice, but do search on Steam forum for any alternative solutions, if there is.

This post has been edited by -ZeN-: Jan 5 2010, 02:48 PM

not too sure about that, but worth a try, since basically u just moved back the folder only i guess. as long as no hidden VAC code that check those kind of things. hrmmm not sure how it worked, anyone tried that?

As usual, do try update your graphic card, or sound card driver to newest 1st. Then maybe you should do an integrity check on mw2 files on steam.

As usual, try update your graphic card and sound card driver to latest.
Then also try to run the game in lower settings.
Also check did your bought the ori 1? (Just asking.)