Almost all OM lenses can be used on the Four Thirds cameras (Olympus,
Panasonic and Leica) using an adapter.  Some work well, some work well
but with limitations, and some work less than well.

That is because OM lenses were (obviously) not designed with digital
sensors in mind, unlike the Zuiko Digital lenses which are
specifically designed for digital with near-telecentric optics.

If you go to the Olympus web site for your country, you will find a
table showing which lenses work best, and with what limitations. There
is surprisingly good agreement between its recommendations and what
Olympus users have found in practice, so it should help you to decide
whether the lenses are worth buying:

http://www.olympus.co.uk/consumer/dslr_OM_Adapter_Compatibilities.htm

Don't forget that the small Four Thirds sensor means that the
effective field of view is that of a lens of double the focal length
on 35mm film.  The 21mm thus becomes an equivalent 42mm; the 28mm an
equivalent 56mm, and the 50mm an equivalent 100mm.  The apertures do
not change.  A 50mm f/1.4 becomes an equivalent 100mm f/1.4, but note
that Olympus recommends using apertures only between f/2.8 and f/8.

All three fixed focal length lenses are excellent performers on 35mm
film.  I have little knowledge of the 35-70mm zoom, but the aperture
range recommended by Olympus suggests that it will not perform
especially well on a digital SLR.

Here's a photo of the kit:
<http://www.edgehill.net/1/?SC=go.php&DIR=Misc/photography/2006-11-25-oly-om-1>

The longer lenses work best, the wider ones not as well.  In fact, an
ordinary digital kit lens works as well at wide mode 14mm than would an
old 35mm lens.  But Olympus has nothing like the 50mm f1.4 now and it
allows for a fast lens on a digital.  The only other alternative is a
Sigma digital 30mm f1.4 which costs about $400.00.  I've compared
longer lenses and the 35mm lenses do have another attribute, they do
not vignette much if at all.
http://www.pbase.com/andersonrm/image/58937829