I'm not really sure on this in the terms of gnutella but as much as I know about resuming files in anyway the counterpart (the node you're downloading from) must also support that feature!
because it has to start transmission somewhere in the middle of the file. if it does not support this it will start at the begining.

as far as i know i had my first 2 source download today and it was pretty cool. unfortunately did one source quit the transfer and i was therefor stuck at 10% with the slower source. i just looked at my search results found the only possible 2nd source on it again. then i killed the slow download and started from the other source. it resumed back at 50%. i know it does not always work but as i said it has to be the exact same file and the other node has to support it to.

regards.