Bumpety bump.
I'm thinking that this might be a hardware issue.
I have my 24" iMac (N-enabled) right next to my PB G4. The router is about 8 feet away, with one wall between the computers and the router.
In Internet Connect, the PB gets full signal. The iMac gets 5 bars (1/3rd signal). This is affecting my speed so much that an ADSL speedtest run from the iMac shows my connection speed as 1.3MB/s when I know I have a 2MB/s connection.
I know the lid of my PB is basically a huge aerial, but there shouldn't be so much difference in signal strength.
Hoping someone will be able to shed some light on this.
Edit: The Apple Discussions are SWARMING with this problem, and Apple are ignoring it like they usually do. If anyone has this problem, please go and make yourself heard, and contact them through their iMac Feedback page:
http://www.apple.com/feedback/imac.html