If you ever need to add a user to a local group on your Windows PC here is a way to do it.
Open and Administrator Commnd Prompt
Type net localgroup <groupname> <username> /ADD
NET LOCALGROUP administrators sethspearman /ADD
Hope this helps someone.
I just used this to add a user as a local admin on a Windows XP since I could not figure out a way to run the Local User and Groups applet using Run As.