DHCP Issue With 10.5.8, Won't Issue IP's

Hoping someone can point me in the right direction here. I've got an iBook running 10.5.8, acting as DHCP/proxy server. However, I can't seem to get DHCP to issue IP's from the pool.

What is odd, though, is that if I create a reservation, that works fine.

Anyone seen this before?

EDIT: OK, the issue would appear to only occur when the iBook has created an adhoc network, and is serving IP's via that. I've just joined an existing WiFi network, and DHCP is working fine....