Runas local user from another machine

All,
I have an app that I'm tring to get to work using a runas
string as an argument for a calling shell script, or
perhaps an API (I'm open to trying anything at this
point). I have essentially two computers. The client
machine is the machine that runs the app. The target
machine is the machine hosting IIS. The app is trying to
use a local account on the TARGET machine as the
credentials for the runas. The client machine has a
custom .msc file for the mmc snap in. The shell string
looks as follows:

runas.exe /netonly /user:<TargetMachine>\<TargetLocalUser>
"mmc.exe "\\<TargetMachine>\<FileShare>\file.msc""

Is there anyway that I can get this to work??? I need it
to work on both XP and 2000. I have a working version
using domain credentials, however I need to get something
using local accounts of other machines. Thanks for the
conciderations in advance!

Jeff