Change User Credentials on Intranet

On our internal IIS server we have a SharePoint site as well as various
other ASP.net sites.  One site is used for ClickOnce deployment of a variety
of Windows applications.

Recently when trying to publish a ClickOnce app to the server, I was
ultimately forced to use the server/administrator credentials because the
server would not accept either mine (domain admin) or the actual domain
adminstrator's credentials.  That's a separate issue.

Now, though I'm not prompted for a login when connecting to the SharePoint
site, I've found that SharePoint thinks I'm the server/administrator, since
whenever I checkout a document, it's shows to be checked out to the
server/administrator.

How can I reset the credentials used with IE upon load/login?

PS.  I've removed the Intranet site from my Intranet domains list and 
deleted all cookies.

Thanks.

Ross