I run a server on my PIII 1G 256MB RAM box on my home DSL connection. I can get up to 8 humans before the server starts lagging. This is the great thing about CSBot, you can run a home server with like 10 bots on and have your own 18 player server! Plus it's your server so you decide the rules/mods! I run Metamod, AMXmodX, HLBooster, and various other plugins for AMX-X. Google 'em.
For more info on CSBot, visit the official CSBot forums:
When bots are being used, it's better to run the server on a seperate box as the bots can take up a bit of memory. Unless you have a really beefy system...