using a W2K3 dhcp server delivering network data for a vlan. Since some days a couple of W'XP and W7 clients won't get settings from the dhcp server anymore. On the dhcp server, such clients produce a NACK with e.g. an ip 192.x.x.x. Connecting the client to another line, i.e. another connection on the router, settings may be delivered from the dhcp server. Setting the client then back to the troublesome line and deleting the lease, again no settings are deliverd by the dhcp server. Any idea, wether it is a problem of the router or the dhcp server and how to solve it?