When seeing the sheets/comments I made above, you shouldn't wonder.
The heap management of Win9x/ME is leaking. When starting Xolox/Bearshare you first see the CPU is running high and allocates a high amount of RAM. If there is not enough RAM, programs do not work (happens to e.g. Irfanview) or the system becoms very slow due to exzesive page swapping. My advice: Spend your computer more RAM (it's very cheap at the moment) or upgrade Windows to Win2000/XP (if you really need to - never change a running system).