Window XP and Radius Authentication

Hello everyone
I don't know if this is the right place but
I have recently setup a Radius Server via IAS to perform 802.1x wired
authentication using (PEAP-MSChapV2) through my Dell PC6224 Switch.
I have tested my setup and I am able to authenticate to the IAS server
no problem and I can access the network when I am in the windows
desktop. However I cannot seem to authenticate to the IAS server
whenever I try to log in from the password prompt screen. I have set
up the 802.1x wired authentication to automatically enter the password
when ever a domain user tries to log in. But when i look at the logs
in IAS it seems to authenticate using the computer domain and not the
domain that the user belongs in. For example it would try to
authenticate to IASTESTCOMPUTER\testuser instead of the domain FORFUN
\testuser. Is there anyway to make XP authenticate via the domain name
and not the computer name?