XP Network Problem

The office has a shiny new PC (Intel 2.4GHz Dual core cpu, 1GB Ram, Leadtek FX1500 256MB OpenGL certified video card.) I can get it to connect to the office LAN and see other PCs/Print/Share files through the DLink router.

I am buggered if I can get it to connect to the net. I've tried all the setup procedures I can think of but I'm not a confident hacker and XP's lack of configureability is beating me. Please throw suggestions at me. ("switch to Mac/Linux" will earn a tongue-poke.)

FIXED!

Many thanks to camstone talvinamarich and especially theweaselking for your help and suggestions.

james_b pegged the problem: MAC filtering for WiFi security. I'd forgotten to add the new PC MAC into the list.

Thanks everyone. Time for a quick snoopydance, then back to work.