oooooo, my favorite subject: HL/Counter-Strike! just had to chip in on this one...
NO - HL (client) has not been ported to linux, though i had read around a year ago that a port has secretly been in development for some time. well, a year later and still no port. i wouldn't count on there ever being a port either. vALVE is notoriously slow in these areas. and since HL hasn't been ported, obviously CS cannot be ported. however i'm told that HL/CS runs quite well under WINE.
saw a few comments on the problems with the HL code. well, that is true. HL/CS is thee most popular multiplayer FPS game there is by a factor of around 2, in spite of the fact the quake based engine is 3 yrs. old, with hundreds of thousands of players on-line at any one time and a 5 million+ player base. when you have something that incredibly popular, poor code or not, it's going to get hacked -- especially in the gaming community where there are a whole LOT of malicious hackers. this is certinly not something specific to CS however. dealing with cheaters is an every day thing for any reputable server admin and tools other than vALVE's anti-cheat software are freely available and manage to be pretty effictive.
if you are looking for quality, mature people and cheat-free servers, there's plenty to be had. look around. and the above statement that "98% of them are cheating" is totally off the mark. that simply just isn't so. yes, there are cheaters, but any half-baked server admin can easily and effictivly deter cheating due to a wealth of anti-cheat tools in addition to the recently developed technoligy introduced by vALVE.