Not sure I've quite grasped where the connections are.
A Wireless Access Point (WAP), yes? Inside, or connected to a router somewhere nearby?
A wireless card in the laptop, yes? (PCMCIA or USB?)
If the WiFi signal is fluctuating on that setup, I would suspect a flaw in the WAP or the wireless card or in the positioning of one of them. Does the signal disappear or improve if you move a few inches closer or further away? (It could it be that you just happen to have put your laptop's WiFi access device in a signal null from the WAP. That does happen - move it a few inches and the signal returns.)
If you take the laptop further away from the WAP, does the signal disappear completely?
Do you have a spare wireless card (even an older 802.11 format one) to check with?
Have you any other device with a WiFi capability (eg a PDA) that can check the Wireless signal? That will tell you whether the problem is your WAP or the wireless card in the laptop.
Can your wireless card detect any other Wireless signals? Mine picks up about four from the houses around us.
You shouldn't need to mess with USB connections like that - wireless access is pretty solid and reliable. Or should be, anyway.