Memory is good, and the more memory you have the happier you will be. In fact, adding RAM will do more than anything else to accelerate your system. You should have at least 16MB of RAM at a bare minimum, and preferably at least 32. Mind you, if you can get a couple of gigs of RAM in your system, OpenBSD will take full advantage of it.
Most weird crashes and unexplainable problems can be traced back to bad memory, so be certain that the memory you are using is good. Memory is the most likely failure point in an old machine.