You'll need an adapter (from ebay usually) to convert the 4/3rds mount to suit the older lenses that you want to use. This doesn't have to be other Olympus lenses either, there are convertors for Minolta, T mounts, even Canikon I think.
From here I think it might be a case of trial and error. Some lenses will work better than others, but from what I gather most of the good primes work well with the 4/3rds sensor. The image quality will not be as good as with a dedicated 4/3rds lens though, as the 4/3rds lenses are designed for the light to hit the sensor straight on. The older lenses will cause the light to fall on the sensor at a slight angle. Still, I haven't tried but know that there are some very good/acceptable results out there.