Windows Server 2003 with DHCP and Vlans in Switch Summit, 2 NIC’s per PC

Hi.
I’m developing a network with DHCP in Windows server 2003, I have a PC that have 2 NIC’s, one is connect to network of my company that have DHCP and the NIC take a IP address without problems and the other NIC is connect to a network with DHCP in windows server 2003 and take the ip address perfect. The problem is that sometimes the PC doesn?t connect to network Applications and Internet Explorer.