Maximum PC

I'll make it short,

I tried to help out a family friend who wanted me to install their wireless router to their wired network. They live in the boonies, and are receiving their current interent from Execulink. The internet is fed to them wirelessly from antennas in the surrounding areas, and onto execulinks modem. I have configured the router with the proper specs and PPPOE, but cannot connect to the the emitting wifi signal I have set up for them. Something is just not getting through.

The new laptop they want to use via wireless "see's" the SSID, and can connect via WEP key, but has limited or no connectivity. Host computer connected to the modem is an old old Dell Optiplex with XP. What am I missing? Tips?

Thanks everyone

Reinstall drivers, maybe? Scan for viruses and malware, too.