geoff,
Found this in a Google search, along with a bazillion other hits....
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Cure for missing msvcr70.dll and mscoree.dll
By Charles L. Smart
Many users who install the current build of the Microsoft.Net SDK complain
that the C# compiler does not work and C# executables will not run. Error
messages note that msvcr70.dll and mscoree.dll, respectively, are missing
from their system directories.
Here is the cure. Uninstall the samples and the sdk. Then restart the
computer in safe mode. These are several ways to do this. The old way still
works: hold down the F8 key during startup until the computer starts
beeping. You will be presented with a list, select 3 - Safe Mode. If instead
you see the desktop, you waited too long, try again.
Browse to the big Setup.exe file that contains the sdk. Reinstall the
Microsoft.Net SDK.
The files msvcr70.dll and mscoree.dll are now in your system folder.
Restart the computer in Normal mode. The csc.exe compiler will work, and c#
exe's will run.