How can I set the priority of DHCP servers to get a lease from in windows (XP)?
As far as I know, a DHCP client just broadcasts a DHCP request and accepts the first valid offer that comes back; there's no client-side mechanism for selecting which offer is "best". There's apparently a draft DHCP option for setting server priority, but the draft RFC dates from 1997 and I can't find it actually implemented anywhere. Depending on what you're trying to do, you could split your DHCP scope among multiple servers; is this for availability/redundancy, or something else?
You can't. First come best dressed.
If you're so insistant on specific machines getting specific IP's, why not just manually assign them?
You can use two DHCP servers and set one to Authoratative, the other not. Only if the server designated as Autohoratitive would not be available would the clients take an IP address from the second DHCP server.