Add RADIUS Server To Network

I have a network that has never had a RADIUS server.  I am looking into setting up a RADIUS server for our network.  Currently our network is wired.  Looking (maybe 1 to 2 years from now) adding wireless networking capabilities.  I am in the process of doing site surveys to determine where to add wireless access points and how many access points.

I didn't know what effect setting up and making active a RADIUS server would have on existing PCs attached to our network and logging into our Active Directory Server.

I know the clients would have to somehow be added or registered with the RADIUS server.  Just unclear to go about introducing a new, never before used RADIUS server into our existing network.

Thanks!