OK This is the function for PRIMARYGROUPNAME that returns the full name of primari group (I use a version that involve .ini file, but works like this)
code:
Function GetPrimaryGroup($Computer,$user)
 
 $UserObj = GetObject("WinNT://$Computer/$User,USER")
 $PGID=$UserObj.PrimaryGroupID
 $UserObj=0
 $domain = GetObject("WinNT://$Computer")
 $domain.filter = GROUP,""
 $GetPrimaryGroup=""
 For Each $Group IN $domain
       $GroupName=$Group.Name
       $AdsiPath="WinNT://$Computer/$GroupName,GROUP"
       $gr = GetObject($AdsiPath)
       $GRID = GetRID($AdsiPath)
       If $GRID=$PGID 
           $GetPrimaryGroup=$GroupName        
       	   Return
       EndIf	
 $Domain=0       
EndFunction
Here is an example of use:

? GetPrimarygroup("SOLE","pagan")

MR. Howard Bullock, any update or other ideas to set PrimaryGroupID?