|Thanks for your response - I'll look into these today.|
In the meantime...
I'd love to update the system but sadly the only way these tills will take a program is via the serial port and we've got in excess of 100 of them. At about £500 for a new system I'm hoping to find a cheaper solution!!!
Any idea if I could use a bluetooth-serial port connector on the till and send to multiple tills this way?