In pgcedit make sure "options > input/output > when saving, leave at least 32k of space between ifo and bup" is marked. In pgcedit you can also set the layer break.
When burning with imgburn you can mark the layer break as seamless.
Edit: There's a very good guide at videohelp (I don't know the link). If you can't find it and need it I can mail it to you (if you PM me you address).