Use the XP network wizard. The two computers must belong to the same workgroup, so you need to set up the second computer with the same workgroup name. Then turn your attention to the wireless connection for which you need to know the name of the network and the password (these are not the same as the router user name and password unless you set them to be the same). Email me if you are still stuck.

Did you turn on the wireless network adapter on the laptop?
Double-click on the WLAN icon in your systray (next to the clock) and check if your wireless network is displayed there. Usually a network will be detected automatically.

If it works on your Vista computer then your ISP isn’t going to help.

You can try adding the wireless network manually. You need to know the SSID and WEP/WPA key though.