Be aware that if it has already assigned IP addresses in the range that you are about to exclude - eg. .2 - .9 in rrambo's case, the client will keep requesting to refresh that lease and the core will keep providing the same IP address even though it is no longer inside the range. Which can be confusing until you realise. Also, because it is now outside the range, if you remove that device from the device tree (assuming it is a file server) the pnp scripts will no longer detect it as it considers it to be outside the IP address range that NAS's/File servers are supposed to be in.
You have to edit the DHCP server's config file to remove the lease (I think this is /etc/dhcp3/dhcpd.conf ??) and force your PC to a static address briefly, then back to DHCP assigned so that it forgets the old lease and stops asking for it to be renewed (this is specific behaviour for a WinXP machine and may not translate to other devices, but an ipconfig /release & /renew is not sufficient)
Col.