steam as in the service that lets you play Counterstrike, team fortress and a lot of other games (not free though) you will get it automatically if you have CS source or Hl2, but if you have standart half life only, dont hesitate.. go to steampowered.com and download it (for free) not only can you redeem your Half Life code there to get a bunch of conversions for the game and 2 expansion packs (blue shift and oposing force) but it also has a handy comunity
my steamID is michel1991
i go with the ingame names:
trashcAn RavAginG Hob0 [nl] (day of defeat: source)
sMokEy-0cel0t (HL 2 Deathmatch
Ace of Spades [NL] (Counterstrike Source)
i hang around the most in CS source in the Shootem servers and C- servers (previously cybernetics, i then went with the name Blackf0x...)
just specify as much info as possible about your steam acount, ktnx
edit: corrected information