They used to make an adapter to run multiple ISA slots off of one slot, however I haven't seen one for PCI. It is possible that you could upgrade your motherboard, but that might be more trouble than it is worth.
Is there anything you can remove from a PCI slot? Such as old modems, sound cards etc.? Also, there are USB2 and fire wire external devices you might be able to substitute depending on what you need. If it is a fire wire or USB2 add on card, you can get cards with types of ports.