This sounds similar to two problems I've had before.

The first goes something like this:

• You PXE boot and DHCP works
• You start the installer
• It times out waiting for a network service (DHCP, NFS, etc)

The problem is Spanning Tree or other network negotiations. When the second attempt to connect to the network happens the switch port has to do it's Spanning Tree negotiation. This can take 30-60 seconds and the service waiting to get a reply from the network times out. The fix was to enable "port fast" on the switch port that the server was connected to; this skips the negotiations that happen. Cisco calls the option "port fast" though it may be different for other vendors.

The second problem I had was a box that had two NICs. PXE boot detected one NIC as eth0 but the kernel detected the other as eth0. The problem has to do with how the BIOS presents the NICs to the kernel and how the kernel determines which NIC is first. The solution was to physically switch ports between PXE boot and the installer doing DHCP. Another option is to disable one NIC in the BIOS. This will have consequences if you re-enable the NIC after you install since the kernel will still detect the other NIC as eth0.