There actually is a way to resume a large file (or a file of any size) without having to dl other programs. Though it's a bit *tedious* to do so.

First, re-find the file and start downloading it. Once it has started, immediately abort it and close Gnotella.

Go to your Temp folder in the Gnotella folder and find the file which is the newly-started one (check it's file size to know the difference between the new and the old).

Copy the name of the new file, delete the new file, then paste the name over the old file.

Reopen Gnotella and hope that the file from the host is still available. If it is, it'll try to Request it and resume it from where you last left off.

It sounds like a lot of work, and it probably is. But at times it can be a great time saver in the long run.