I am experiencing the same symptoms as found in this question:
Win2K SBS. DHCP says it's out of leases, but when I look at active leases, only a handful are there. I have tried restarting the DHCP server service and refreshing the console - to no avail. The lease time is set to the default 8 days. Scope size is 51, only 8 leases are listed. There are no reservations or exclusions.
An interesting thing I do see is that BOOTP is enabled, though I'm not sure why. There aren't any BOOTP images or options set.
Any idea where I can see these used-up leases and clean house?