Here's what I do, and it workd part but not all of the time (and requires some serious determination):

If a download has stopped (either says downloading but is staying at 0 KB/s or has begun but then lost the connection and gone into endless requery) then do searches -- multiple searches if necessary -- for the same item; you can try different permutations of the artist and/or title. Don't re-download them, just do searches. This will, due to the branching and ever-shifting web of peer-to-peer connections in gnutella (as I understand it), get you linked back to the place you originally found that file in the p2p network, IF that person is still on line and the aether gods are with you. I have forced dozens of files to resume this way, but many more than that have not -- too many factors, too little time... But if there is a particular file or set of files you really want, this is one way to get it. And in general big searches make your connectedness more "robust," or so I am told and it seems to be true.

We shouldn't "abuse" this, as too many searches can bog down gnutella, but I'm sharing 10,000+ files and figure if I really need one back, I'm entitled to poke it with a few extra searches until it comes down.

Hope it works for you!