I am exporting my outlook calendar to excel and whilst with a very small
date range it works ok, with anything over a few months (there will be a
hundred or so appointments per month not thousands) Outlook seizes 97% of
the processer
and the export dialog just sits there with one bar on the progress meter.

I have tried the same with an Access export and even the smallest export
siezes in the same way immediately.

The export translater software was installed for both Excel and Access
apparently successfully and the machine re-booted as well more than once.

Has anyone any thoughts on why this might be?

The Outlook export does seem to have some quirks.

If your not happy with the results your getting, consider using
WinCalendar.
It is a Calendar Maker that can convert your Outlook calendar into
fully formatted calendars in both native MS Excel & Word format.
It supports many layouts & options.
For more info see:
http://www.wincalendar.com/calendar-maker.html
http://www.wincalendar.com/Outlook-Calendar-Import.htm

Enjoy!
Mike