I had the same problem just today. What I did, if you have the latest XBMP/XBMC, edit the XML file where it says <UseFDrive>yes</UseFDrive> now right after that, there should <UseGDrive>yes</useGDrive>. If there isn't, pop it in there.
Now, you need to head down to each section (inside the XML file) and make a bookmark to the G: drive. So just copy and paste a bookmark of say your F: drive and just change the name to G: Drive and change thepart after <path> to G:\ instead of F:\ and bam, found! Sorry if this is a little wordy I'm having a tough time with my soberness.
