If you have not already done so upgrade to GBPVR 97.13, and convert to the SQLlite database. This database will remain nicely clean, small and responsive.
This ever growing database was one of the main reasons we're moving to SQLite. You can use the ChangeDatabase utility to switch over.
Access databases do not reclaim space even when data is deleted, so are constantly growing. It is possible to compact a database under certain circumstances, and GB-PVR will try to do this, but there are many situations where this is not possible.