Wait... is your problem that Windows freezes or that your router freezes? This thread is about router crash issues.
"the game freezes." (quoted from the OP).
This thread is about router crash issues.
The threat title seems to be "Re: Multiplayer problem : joining server = game freezes"
For the Windows problem, try to check OpenArena installation folder user permissions; if you need help, please open a specific thread, specifying if you have XP Home or XP Pro. And are you sure you are using a "guest" account, or do you simply mean a "user" (not with administrator priviledges) account?
I'm not asking for help, I'm trying to offer it. Thanks though.