Bearshare has installed a lot of ad, spy and "foistware". I don't know how much of it you can remove without affecting Bearshare, but I think you should dump it all.
My recommendations: Go to Add/Remove programs and remove, one at a time and rebooting after each removal:
New.net
SaveNow
If you see Web3000 there, remove it also.
Go to this site, read the FAQ and click on the Download Ad-aware link.
http://tomcoyote.com/lsindex.html
Then download Ad-aware 5.62 and the Ad-aware Signature file (zipped) to a host folder.
Run the Ad-aware install, then unzip the reflist.zip and copy the
signature file to the Ad-Aware programs folder to overwrite the previous one.
Run Ad-aware and configure it to scan all drives on which you have installed programs, memory and deep registry. Check everything it finds, click "make backup" and Finish.
Then reboot and run a second scan to ensure complete removal
This is likely the major culprit, but we really need to run ad-aware to make sure all its components are gone:
msbb Registry (Per-User Run) C:\PROGRAM FILES\N-CASE\MSBB.EXE
I believe it is causing the IE5.5 browser window to close by trying to open a pop-up add in a new window.