Are you using WEP encryption on your Router and Laptop? Have you selected XP to manage your WiFi connections? Have you checked for any Firmware updates on the Netgear web site?
The fact that your laptop worked at the retailers and the engineers worked at your location suggestd the problem is obscure!
How about a complete reboot of the Router, or even a complete Reset, and start afresh? I think going back to factory defaults and seeing what happens as you enter the correct settings might be a way ahead.