The number one possibility is ZoneAlarm. That thing has
never been strong enough to keep up with BearShare on a
broadband connection, often resulting in freezes and blue
screen crashes.

Try uninstalling it completely and reboot before trying
BearShare again. If that does the trick you can get a solid
firewall for free at this site:
http://smb.sygate.com/products/spf_standard.htm