I had to do this in a live situation this weekend.
For Sympana 10 this is what I had to do:
On the File System sub-client browse a backup to System State > Components. One of the objects on the right will be Sysvol. You can't "browse" Sysvol to select specific objects such as GPOs. You have to restore all of Sysvol, to a different location. And then in that location find the GPO that you need.
I don't know about earlier versions of Sympana but, with v10, if you just browse the backup for File System sub-client, and browse to Sysvol, the sub-folders are there but they are ALL empty. Gotta use System State.