General Signal Strength Question

I'm having signal strength issues with my Linksys WRTP54G. I've got it on channel 11, and I only get 48% strength 2 rooms away. I even have a stronger antenna attached to it. What really confuses me is how I'm getting stronger signals from at least 3 other networks, none of which are on channel 11. In fact, channel 11 is the least crowded of channels 1, 6 and 11, which i understand are the preferred ones. There's one other network on channel 11, but it's down at 23%.

Is there anything I can try to boost this signal? I know this is pretty general, so if you need more info, I'll be happy to post it. Thanks.

There can be many things the cause signal problems. Check out this link for some basic tips on what to look for.
http://www.gowifi.co.nz/linksandinfo.html

Good Luck
Dale