Did he set a static IP address in the properties sheet for TCP/IP?
If so, he may have set the address in the DHCP scope of the Linksys router, a no-no for that particular router.
Assuming default settings on the Linksys, he can either:
1. Set the TCP/IP Properties sheet to "Obtain an IP address automaticly" and clear any Gateway and DNS entries that were entered manually; or,
2. Set a static IP outside the default DHCP scope of the Linksys.
Go to the properties sheet for TCP/IP and:
Set the static IP to 192.168.1.2, Subnet 255.255.255.0, Gateway 192.168.1.1
For the DNS entry enter nothing, or 192.168.1.1
If you network, while there he should it the "Advanced" key and under the WINS tab disable LMHOSTS and enable "Use Netbios over TCP/IP."
If any port forwarding entries were made for Games or ICQ they should be modified in the router's setup to reflect the different IP address he will now be using.