|You put Windows XP as the OS. That field is for the OS of the problem computer.|
You said there doesn't seem to be a DHCP box to tick. Where did you look?
Do you have a Internet Protocol Version 4 (TCP/IPv4) or similar entry in your LAN Properties? If so, the entry to obtain the IP Automatically should be checked in the Properties.
If it's set to DHCP and still not working, Look here:
Life's more painless for the brainless.