NetBios-style TO DNS-style

Hi,

I've Win2008 server with multi sessions users logons.

I query each session for the username + domain name.

When I query for Domain (via WTSQuerySessionInformation) I only receive NetBios name-style (i.e domain)

My question is: suppose I have the username + NetBios name, How can I retrieve its DNS name-style??

one important point, the logon of different users are remote desktop logon.

if I've the logon details in the form of domain\username (SAM), How can I convert it to username@domain (UPN) ??