Just go to My Computer properties -> Device manager and see if you have there any unknown devices or more than one network device, one of which seems to be wireless.
Or post here your motherboard model, processor type and tell if you have any extension cards with antennas.
ashgreeves wrote:Board: FUJITSU SIEMENS MS-7293 1.00 1.87 gigahertz Intel Core 2 Duo Windows XP Media Center Edition Service Pack 2 (build 2600) no adapters with antennas
Your motherboard is manufactured by MCi. It seems not having any embedded wireless features. Or rather to say that I could not find any.
So, my conclusion is that you need an additional WLAN card (external USB stick or internal PCI version) to have your wireless network working on your computer. They are not that expensive. You can get one for 15-20$ or even cheaper.