To see user names, you should authenticate your user with squid.
If all you want is to know who went where, you should:
1. link netbios names to dns
2. resolve fqdn in squid
3. use sarg defaults
For 1, you could assign static ip with hostnames panel or install dhcp-3
2 is a simple change to squid config
I'd write an howto, but it's still hard to find time
If you volunteer, I can help you.