I would start at Cisco.com with your router model's documentation. That router should have two Ethernet ports -if I'm right, that makes your job a little easier. Unless of course you're using one to connect to a high-speed cable modem. One ethernet port should already be connected to a switch. If you're using a Serial interface for your Internet, then you should have an ethernet available.
Setup is going to depend on your exact model's documentation. I'd download that from cisco.com.
But, ideally, what you want to have is VLANs and a Routing Protocol with your two networks. Your router interfaces would be configured similar to this:
Ethernet0
ip address 10.10.20.1 255.255.255.0 (assuming you've subnetted down to a class C)
ip helper-address 10.10.21.xxx (whatever your dhcp server is)
Ethernet1
ip address 10.10.21.1 255.255.255.0
ip helper-address 10.10.21.xxx (whatever your dhcp server is)
You're also going to need to configure your routing protocol on the router (rip, igrp, ospf). Let me know what you're using and I can point you in the right direction on that as well. Here's an example of how to configure RIP:
You're also going to need to put your switchports on your 2900s in different vlans based on whether you want them in your server subnet or your workstation subnet. You can find documentation for doing that here:
If you can borrow a CCNA book, or even better a BCMSN book, from one of your Cisco pals, this type of setup is generally found in those books.