Try turning partial file sharing back on, and test by downloading one of the free videos from a reliable source like magnetmix.com (The Scene episodes are pretty popular and should fill your max download speed of 64 KB/s). Turn PFS off and try again.

Also, check the sample bug reports to see if your machine can accept incoming connections. If so, setting the OS X firewall to allow gnutella connections on port 6346 should help.

btw--high initial spikes in speed followed quickly by low averages, then another spike 30 or so seconds later might indicate that your bandwidth is being choked--often by ISP controls. Watch the download bandwidth graphs in Tools->Statistics