Layer 2 to Layer 3 migration – Where do I start?

I’ve been tasked with migrating our current layer 2 flat network to a layer 3 routed network. Our environment consists of a mishmash of Cisco Catalyst, 3Com layer 2 SuperStacks, and 3Com layer 3 switches. I’ve created the necessary VLANs on all switches and I’ve devised a new IP addressing scheme for all devices. I’m using a stack of Cisco Catalyst 3750Gs as the core switch, and DHCP is currently being handled by a W2k3 server. However, this is as far as I’ve gotten and am now at a loss as to how to proceed. One of the biggest hurdles I’m looking at is how to configure DHCP to assign addresses across the subnets. This is my first migration of this magnitude and any input/ideas are greatly appreciated.