Hi Jorge,
Are you going to use Microsft 2008 server as NPS ( radus server) or are you trying to use ACS as your radius server.
If you are going to use ACS as your radius server you can generate self signed cert on ACS server and use it as your Radius server.
But if you want to use Microsft 2008 server as NPS ( radus server) you may need to find out from Microsft if your NPS server itself can generate a SSC to work for PEAP.
Cheers,
Srini