Have I been hijacked?

I can’t seem to change the startup using msconfig. I get a message saying I need administrator rights. I am the admin.

When I go to cmd>Net User I get the following: Administrator ASPNET GUEST
HelpAssisrant IUSER_MARK IWAM_MARK
ms support_388945a0

When I log onto (Windows XP Pro SP3) I see only MARK, me, the supposed admin, and a guest account. I click on MARK and enter my password and Windows boots up. Why is ASPNET showing as the admin when I use Net User? Thanks