Setting Fixed IP Doesn't Take

Vista Business, wireless adapter. Works perfectly with DHCP enabled.
I tried to set a fixed IP (IVP4) for the NIC.
Vista keeps resetting the subnet mask to 255.0.0.0 from 255.255.255.0
I go back to reset the subnetmask with EVERYTHING entered and then Vista
wants an IP address. But it's already there. I retype the IP, just to help
Vista. No good. Keeps asking for an IP

So I can't set a fixed IV4 IP address. Any help welcome I can see all the
entries in regedit and think my only recourse may be to do the changes
there... sad if true.