Wireless connection speed

[chicken10der]

I know how ridiculous wireless networks are to troubleshoot through a forum, but I thought it would be worth a shot just to see if anybody has anything I could try:

I have a Linksys WRT54G wireless router and use Windows XP. Most of the time, the Connection Speed is 54 Mbps (from the wireless connection tray icon). However, at seemingly random times, it drops dramatically. It can go to 36, 24, 18, 11, 5.5 or even 1 Mbps and my internet connection slows to a grind. The signal strength is always Excellent, and I use WPA so nobody else can use my connection. Any ideas what might be causing the slowdowns or how to get the speed back up after it drops?