The first question is, what type of mount does this lens have?
If it's a T-mount, you'll need a T-mount to 4/3 adapter (personally I use a T-mount to OM adapter and then an OM-4/3 adapter with my 500mm T-mount lens).
If it's anything else, you may be stuck.
The one's I've seen on ebay often state "T-mount adapter for Olympus included" and or "MF-1 adapter included". I already own the OM-4/3 adapter. My question is more about the quality of these lenses. Are you an owner of Opteka lens? Can you share some pics?