If you have any other accessories, such as translucent pattern blocks, then you're perfectly set up. I bring out the overhead projector as an actual party activity, especially for little siblings or friends on the younger side of the guest list, but my own girls will still spend entire quiet mornings or afternoons engrossed in play with the projector.
Only rarely, outside of helping out with some academic activity related to one of their areas of interest, do I set up an actual "activity" involving the overhead projector, but I was so delighted to see on Play at Home Mom that some other parent besides me is ridiculously fond of a projector that I invited Syd to create the overhead projector Christmas tree from that site.
She drew a tree on a clear plastic page:
She set the page on our projector, and decorated it with translucent geometric shapes:
She enjoyed its projection on the wall--
--before taking it all apart and doing it again!
Unfortunately, we only have a small amount of wall space suitable to using the overhead projector in our living room, although as wall space it is ideal, since you can tape a large piece of paper onto it and copy from the projector:
...oh, and a much larger wall space for the overhead projector.
For this project, we use: