Ever since I've been running Vista on my primary laptop I could never find out how to get a runas command working for my domain admin account (my normal logon is non privileged). Ran into a post on windowsconnected.com which explained about changing the GPO setting for elevation prompts from prompt for "consent" to "credentials". As Josh notes, this will now prompt you for credentials for anything local as well. It's a small pain and hopefully someone (ahem Microsoft) will allow for some better flexibility at some point.

Check out the post here, http://windowsconnected.com/blogs/joshs_blog/archive/2006/12/01/windows-vista-tip-run-as-administrator.aspx.