router/nat with only one NIC

[Tim Wunder]

Is it possible to route internal internet traffic through a server that 
has only one NIC?

I've only had one PC connected to the internet for quite some time and 
have it configured to route all internet traffic through squid, 
squidguard and dansguardian. I want to add a second PC and have its 
internet traffic routed the same way. The server that runs squid and 
dansguardian currently has only one NIC. So far, the information I've 
found on the 'net through googling indicates that I need to have a 
second NIC in order to do this.

Is there a way to do it without adding a second NIC?

I know... NICs are cheap, just buy a second one. It'll just be a pain to 
have to pull the server out from where it is, then install and configure 
a NIC. I'm trying to avoid that.

Thanks,
Tim