Background: I'm trying to call LaTeX from Squeak using OSProcess, so I
can have nicely formatted maths formulae, using LaTeX preview mode and
Ghostscript to generate PNG files from the PDF that LaTeX produces.

But I'm stuck trying to invoke a command such as pdflatex.exe from
Squeak in a directory of my choosing. 

So, having created a temporary directory, how do I run my command in a
sub-process with that as the current directory?

cheers,
Simon