What you're talking about is something we do in several Customer sites (including a school District who appears to be doing exactly what you want).
This isn't a click-for-click guide, but if you don't mind playing around with the tools a bit I think you'll find they're fairly self-explanatory.
The IAS server will need a certificate installed as a pre-requisite to performing EAP. If you don't mind using a self-signed certificate (which we're doing everywhere w/ no major issues) you can install Microsoft's Certificate Authority and the IAS machine will request a certificate automatically (assuming the machine hosting IAS is joined to a domain in the forest with the Certificate Authority). Reading about the best practices suggested by Microsoft re: the Certificate Authority is a good idea (particularly the parts about what can't change after you create your CA), but if all you're using your CA for is EAP you could probably get away with decommissioning it and starting fresh if you ever needed to.
Once you've got a certificate installed in the IAS machine, you need to configure your RADIUS server to accept requests from your wireless access points (RADIUS clients). The Microsoft RADIUS server (at least in W2K3) isn't very good about handling DNS lookup failures effectively, so, much as I hate to say it, I'd recommend using the IP addresses of the APs when creating the RADIUS client entries on the IAS server. The "shared secret" is the value that the RADIUS client (the AP) uses to authenticate to the RADIUS server (IAS). Be sure that you enter it identically on both the AP and the IAS server.
You'll need to create a remote access policy on the IAS machine after you've defined your APs as RADIUS clients. The built-in wizard can do a good job of creating a policy for you. Basically, you want a policy that matches "Wireless - IEEE 802.11 OR Wireless - Other" and, if so desired, a specific Windows group containing users who will be granted access (like, say "Domain Computers" or "Domain Users"). The wizard can guide you thorough this process.
Once you've gotten the policy created you can attempt to connect from a client manually. I'm only discussing configuring the Windows built-in Wireless Zero Configuration (ha!) service here. If your WLAN NIC has a third-party configuration manager and you can get away with removing it I would. Using the built-in Windows service makes the odds of getting the NIC to come up and authenticate properly during boot (assuming you allow "Domain Computers" access in your RADIUS policy) much greater. (I can tell you that I have a large number of wireless clients at my school district site that never plug into wired Ethernet but are able to process group policy, etc, with no problems.)
The procedure varies a bit between Windows XP and Windows Vista / 7, but basically we're talking about going to the list of wireless networks, adding the SSID of the new WPA-RADIUS protected network (remove the old one if you're re-using your existing SSID), and making sure some properties are set properly. The "Network Authentication" should be set to whatever combination of WPA/WPA2 and AES/TKIP you configured on your AP. (Personally, I'd use WPA2-AES if you can, but WPA-TKIP is the lowest common denominator and is supported by older clients.)
In the authentication properties for the new SSID, be sure that "Protected EAP (PEAP)" is selected as the EAP type. If the client isn't a member of your domain, go to the the "Properties" dialog for PEAP, uncheck "Validate server certificate", go to the "Configured" dialog for "Select authentication method" and uncheck the "Automatically use my Windows logon name and password (and domain if any)", and uncheck the "Authenticate as computer when computer information is available" under the "Authentication" properties of the new SSID. This will force Windows to prompt you for credentials on a non-domain-member computer.
Once you get a client "talking" I'd recommend deploying the SSID's settings using group policy so that you don't have to "touch" any clients. I love this functionality and have used it in many sites to great success. As long as the new domain-member client computer is allowed to apply group policy once on a wired network it will "just work" once it's put in range of the wireless network. Nirvana!
For non-Windows devices (iPods, Linux netbooks, Android phones, etc) you'll have to work thru the configuration of the connection yourself. It's not too bad, though. We've got a variety of devices authenticating to WLANs configured in this manner just fine.
Edit:
On non-domain-member computers you'll want to untick the items I describe in my above to prevent the client from validating the server certificate and trying to authenticate automatically. The user will have to manually supply their credentials.
In terms of automatically deploying the configuration profile to non-domain-member clients you can use the "netsh wlan" command on Windows Vista and Windows 7.
On Windows XP, deploying WLAN configuration without Group Policy is really similar to Vista, but requires installing software.
