Windows security

For Win2k, xp, 2003 and possibly vista.

My app used to run in the security context of the user that is currently
logged into the system.  It worked fine until they started giving users a
limited user account.  My app needs to have access to a shared folder that
is only accessible by certain domain accounts, is there a way to
programmatically login to the domain as that account when I need to access
that folder and maybe logout when I am done?

thanks.

-
James