Control Panel, Administrative Tools, Computer Management, Expand Services and Applications, Expand Internet Information Services, Default Web Site -> Properties(Directory Security Tab, Enable Annonymous Access... Insure Checkbox is checked and allow IIS to control password... Default UserID will be IUSR_YourComputerMame (IIS Install usually adds this user, but check it out)
If that doesn't allow access - somethin's been changed somewhere!!!
That's the admin drill down, tis pretty straight forward... and applies the defaults for the individual Webs(directorys) - which may have individual settings...
Have fun drillin...