Try this, just as an experiment for the time being to see if we can get past this issue and maybe better understand the actual problem.
On the Win2k3 server, right click on My Computer and choose manage on the left side expand local users and groups, select users, right click and choose new user. Now add a new user and call him TestUser give him a password of P@$$w0rd unselect user must change password and select password never expires. Now once that is done, double click that user in the right panel and on the "Member Of" tab choose add near the bottom, click the advanced button near the bottom, and then on the find now button near the middle on the right the administrators group should be highlighted so just click OK. Now once that is...