if you have seperatet your users into groups you can use a the following codesnippet as an example:
If user.IsInGroup("GROUPNAME") Then
Bug_Fields("BG_USER_31").IsReadOnly = True
Bug_Fields("BG_USER_32").IsRequired = True
Bug_Fields("BG_USER_33").IsVisible = True
End If
if you want to set the rights for a specific user use:
If User.UserName = "USERNAME" Then
Bug_Fields("BG_USER_31").IsReadOnly = True
End If