wireless network woes

Please note, I'm no expert in wireless networking. I have a main computer running XT that has a Siemens wireless router/high speed modem that is supplied by Bell, I have another computer in my kids room that is only about 10 feet away with a wireless card. The computer in the kids room is plagued with sudden disconnects from the wireless internet, and frequently cannot even find the network. I have tried several wireless cards, both internal, and external USB, and have even tried external amplified antennas, as well as all the transmit channels on my router. Several months later, and about 100 calls to various tech support, still no connection. NOW HERE COMES THE INTERESTING PART: I recently acquired a HP laptop, that has a built-in wireless card, and it immediately connects to the network, without hesitation, and NEVER EVER disconnects from the internet. I can be in the kids room, or half way down the block, and it still works. So, considering the fact that I've tried many different types of wireless cards, both internal, external, using both the internal "slots" and external USB, would it be logical to assume that the problem must be in the kids computer????. If so, where should I look? Any help would be greatly appreciated Thanks Kim "the man with a girls name, and Frankenstein's body"