DNS problem

I have been having some problems with DNS server ever since I upgraded from NT 4.0 to Win2k. Everytime when my users log onto the domain and tries to go to the intranet, the names are able to resolve to ip.. but after a while, things get wild… it doesn’t work anymore… now i have to ask the users to do a ipconfig /renew to make it work again, but this should be the case, anyone has any suggestions or similar problem?