Try the following:
1. Reboot your DSL modem | Router | PCs in that order.
2. Can you Ping the router from your SP2 PCs?
3. Have you tried releasing & renewing the IP address for your SP2 PCs?
4. Is the default Gateway set to your Router?
5. Does connecting the DSL Modem directly to the SP2 PC lets you connect to the Internet?
6. For the WiFi SP2 PC did you try and scan for available wireless networks and then connect to your Linksys?
7. Check the WiFi settings to make sure that the Channel is the same as that of your Linksys Router wireless network.
8. Did you enable WEP and set the encryption key?
9. Can you access the Linksys Router from the SP2 PCs?