slow mounting server and DHCP

When I tri to connect to a server (on local network, independent on os x version) I need to whait one minute or more until it will be mounted on my macbook (10.6.8). Others machines mount the server very fast.

I tried to assign a static IP to my machine in preferences outside the dhcp ip range. The mac mount the server very fast but I can no more access internet and it is how if the router dont accept my IP. (If I use an IP in the dhcp range there is no difference and the server mount sloooow but internet work).

I don't know if this help understanding the problem, but on the routing table of the router (acting as dhcp server) I see my IP and my computer name but for others machines there is the ip adress instead of computer name. I think this could be a trace of conflict in network trafic. DNS server is correct setup but if I set manual IP outside dhcp range in preferences network there is no soubnet mask appearing.

My question is: how to have both speed mount and internet? (I know, should normally work but there is some conflict I can't find).