Slow log on to network in mornings (dynamic IP)

Hi guys,
I work in a office of around 40 users (Win XP + Win server 2003), with dynamic IP. The problem is with user's logging onto the domain in the morning, as all employees need to ?clock in? on a time management system, we are getting a lot of complaints that it takes up to 5 minutes to do this ( the users are not happy about losing 5 minutes ) When you first logon the desktop appears straight away, (not stalling at applying personal settings) but the LAN connection does take awhile to ? acquire IP address? I have set a ?preferred DNS server? IP address on my own workstation just to see if this will help, but I am experiencing the same issue. Is there anything that you could recommend? Any tips are greatly appreciated. Thanks for your time.