running same cs server on two networked comps?

hi, sorry i posted in the networking + lan parties place, i just read the sticky very sorry.

but anyways my friends and i decided to have a lan party but i had past experiences with connecting two networked computers on the same cs internet server. they both have their seperate accounts and running winxp /w sp2. my internet is earthlink cable and a netgear wireless router. could this problem be in my router settings? or windows? thanks