After some thought, common sense prevailed and I decided the MAX3232 device would be the way to go. I got a little board, with an smd chip and the capacitors, on eBay cheaply. So far I've just stuck all the bits on a breadboard, that is a USB to TTL adapter and a DB9 connector, and this now all works fine. When I have the time I'll put it neatly onto a piece of Veroboard, might even put it all in a nice little box!
Now all I have to do is get to grips with the ancient MICE box of tricks and start tracing code...
Thanks for all the assistance from everyone.
