I just bought a Hawking Technology 6-db hi-gain wireless -b/-g antenna from Newegg:
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It solved all of my connection problems. It's amazing. No more disconnects. No more wild signal strength fluctuations. I connected it to my WMP54G internal wireless adapter, set the antenna on my desk, and my Linksys wireless-g network connection has been running rock solid all evening. That's the best $33 I've spent in a long time.