is it free to play online or do you have to reg and pay a monthy fee?
Completely free. The only payment involved on Steam is that you can choose to buy the games on it rather
than from a shop (though you don't get a box or CD, which is pretty much a negative). No monthly fees.
I might try that demo out as long as it's free and all, although i'm not sure about your first point kupoartist, my sister has the Sims 2 and i'v only ever played it once, the reason for that being everything moves infuriatingly slow, it takes about half an hour to load most things, it jumps about, even when you've finished playing the computer continues to move the pace of a snail, and that only time i played it it gave me such a headache (brought on for the above reasons) i could only play it for half an hour. And i'm guessing this is to do with it's system requirements
If it has trouble playing the Sims 2, it is quite likely that you'll have trouble with HL2 (nice example screenie
). That said, it's always worth trying these the demo out to give yourself an idea of how / if it'll run. Remember, that if you get bad performance, you should have the settings as low as possible... if you can cope with how much more ugly it is...