Yay, seems I first have to correct you: Magnet-Links have nothing to do with G2 specifically, other than that they are usable with G2, that is.
A magnet link is some kind of a universal resource-link, which at the least has to include a sha1-hash, and a file-name or directa direct resource link.
You can create those with Phex by using the hash, you find in your shared-files file.
A magnet link is structured as follows:
<a href="magnet:?xt=urn:sha1:HASH&dn=FILE-NAME">link-name</a>
You can add:
&xs=http://YOUR-IP:PORT/uri-res/N2R?urn:sha1:HASH
Comment: you can also use dyndns-servies instead of YOUR-IP, but you have to supply teh port your Program uses.
&as=http://HTTP-URL-TO-THE-FILE
That's it for starters (tehre are some smaller quirks still).
The file-name will be used for searching for the file on the GNet, so it is best to use the original file-name.
The HASH is the hash associated with your shared files.
Best wishes,
Arne