I'm not sure about your Speedstream model, but your apple basestation will have a NAT firewall. Did you check the link I gave to enable UPnP on it (apple calls it NAT-PMP.) Also if you have OSX firewall active, did you configure it to allow LW full access. Get these issues out of the way 1st & perhaps we can narrow down the problem ... or perhaps the firewall issue is related to your problem. Check the 2nd link I gave in my 1st post.

If you use the resume/find sources function on all your files simultaneously then this can put pressure on LW's resources & your computer's resources if there's many incomplete files.

I would also recommend updating to Java 1.5 & forcing LW to use Java 1.5; http://docs.info.apple.com/article.html?artnum=301073
That's update release 1 but there's also Java 1.5 release 3. Java 1.5 will improve LW's performance.