Your DSL will only allow 10 players at stable pings. I know alot about running HL servers (CS mostly) and a 300 upload speed will get you 10 players.
-Edit-
Sorry, I now see 700 upload. Me can't read🙂 Ok, well a 700 should allow 20 players easy. Hope it goes well for you. You could get away with Duron700, 256MB RAM for it. 512MB would be much better though.