One thought is to verify that a firewall isn't blocking you.
Another thought is to verify that your new system is setup the same way your other computer was to network. Did you go through the Network Wizard in XP?
What kind of operating system were you running before and what are you running now? What is your wife's system running?
First, let's try to analyze if you're able to ping the router, in your computer click on start > run > type cmd or command then ping your router i.e. ping 192.168.0.1. If you're able to ping it, it means that you've a good connection with the router. Now our problem is your wife's computer. You're going to connect it wirelesslessly. When you're configuring wireless connection between the router and the client, makes sure that you're using the same Security i.e. if the router is using WEP, the client (your wife's computer) should also be using WEP, same SSID and of course should have same frequency i.e. 802.11A or 802.11B/G.