In case no one else has come across this one yet....
Server 2003 DHCP breaks when you reach the 87th reservation.
Why! I hear you all ask do you want 87 reservations?
Because it's the easiest way of making all your static devices keep programmable network addresses thats why...
But, due to a bug in 2003 server (there is a hotfix but it won't be included until SP2 and it's still being regression tested) when you reach reservation 87 your DHCP console breaks and you won't be able to open it!
Using the command line net sh as described here you can set a bogus reservation and voila everything works again.
This has to be one of the most bizarre DHCP issues I have seen to date.
Hope everyone who reads this logs it into the memory banks!