We have SBS 2003 without ISA. DHCP will happily issue leases to clients on the domain. It will not issue a lease to a client that has not been added to the domain, eg my laptop, or other nodes, eg a network fax.
I have tried giving my laptop and the fax (which is ny preference long term) a static ip from both the same subnet but not the scope, and a currently unused address from the scope, but no joy. Cannot even ping the server. They’re all plugging into the same switch so nothing in between to block traffic. Have switched off all firewalls on my laptop as well.
Have tried rebooting the server and clients, you know, just in case.
DHCP is definitely running because domain PCs get addresses everyday. My laptop used to pick up an IP address quite happily. I cannot think of a single thing that has changed. Everything I’ve found to do with DHCP and SBS is ISA related, but we don’t use it.