FreeRADIUS as proxy to Windows IAS

Hi I'd be grateful to hear from anyone out there who has got Freeradius (on a Linux box) running as a proxy server successfully validating usernames and passwords against a Windows IAS server using the MSChapv2 protocol. I have the Freeradius server up and running on CentOS 4.5, but can't get it to validate against the IAS server successfully. Please feel free to contact me off list. Thanks in advance. Clive