Originally posted by Ideas Man
Runas only works for executables, not files or folders.
RUNAS USAGE:

RUNAS [ [/noprofile | /profile] [/env] [/netonly] ]
/user:<UserName> program

RUNAS [ [/noprofile | /profile] [/env] [/netonly] ]
/smartcard [/user:<UserName>] program

/noprofile specifies that the user's profile should not be loaded.
This causes the application to load more quickly, but
can cause some applications to malfunction.
/profile specifies that the user's profile should be loaded.
This is the default.
/env to use current environment instead of user's.
/netonly use if the credentials specified are for remote
access only.
/savecred to use credentials previously saved by the user.
This option is not available on Windows XP Home Edition
and will be ignored.
/smartcard use if the credentials are to be supplied from a
smartcard.
/user <UserName> should be in form USER@DOMAIN or DOMAIN\USER
program command line for EXE. See below for examples

Examples:
> runas /noprofile /user:mymachine\administrator cmd
> runas /profile /env /user:mydomain\admin "mmc %windir%\system32\dsa.msc"
> runas /env /user:[email protected] "notepad \"my file.txt\""

It does work for files indeed, i havent been able to make it work for folders yet.