drops DHCP lease

Our DHCP server is set to lease ip addresses for 30 days in the 172.16.x.x range. But our Windows XP machines will assign their own ip addresses (192.x.x.x) when it can’t connect to the DHCP server even when it has a current lease for 172.16.x.x. Our other workstations (win95&98) will continue to use the leased ip addresses. Is there a setting I can change on the XP machines to use the leased ip address even if DHCP server is unavailable?