half life 2 in linux

Yeh, Kinda.. using WINE.. but Don't expect it to Run Fast and smooth..

*appdb.winehq.org/appview.php?iAppId=2095
*appdb.winehq.org/appview.php?iAppId=1163

there is no linux version of hl-2 till now but hopefully one will come
well check out this site. made only to handle linux games *linuxgames.com/

Besides using wine you can buy cedega. It is a bit more optimised. But, that is only for hard core gamers. If you are a casual gamer, wine should do for you.
Also, take a look at Frank's Corner for some more info on wine.