assembly search path

I've a shared add in written in C#. It works on the dev machine fine
with VS2003 installed, but not on a machine without VS.
We've been doing lots of research, and my current concern (discovered
using filemon) is that it looks in the app base directory. In this
case the app base directory is the home of Excel.exe. I can load my
application specific portion of the add into a seperate appdomain and
set the dll path from there, but then I have to marshal the Excel
application object across, and I have yet to figure out (try) that. It
seems unnecessary as it all works a treat on the dev machine. Both dev
and test machine have admin rights.

So question one: Is there a way to encourage my add in to look in its
directory, not the app's directory for the DLL's?
question two: what is different between a machine with VS installed
and one without (barring the obvious)?

Cheers

.