I replaced my Lexmark 1100 printer with an Epson 870. I connected it into the parallel printer port of my Umax Astra 1220p scanner where the 1100 had been living and working quite happily. The printer works all the time but if I go to use the scanner I get a windows message Fatal Exception 00 at 0028:C162C498 in VXD PPSCAN(01)+ 00005DD8. If I reinstall the scanner it works for the duration of that session only. Can anyone help me before my whole system gets a final Fatal Exception with a sledgehammer.

Have you tried the latest drivers from www.epson.co.uk? It sounds as though the Epson driver is more rigorous than the Lexmark one in checking that the printer is present all the time.
Failing that, does the 870 have a USB port? Or maybe it's still possible to buy additional parallel port cards...

Yes, you can still buy parallel port expanstion cards -- I looked into it a month or two ago (see www.dabs.com). Another option is to buy a USB to parallel convertor from Entrega (www.entrega.com).

The Epson 870 does have a USB port in addition to the parallel port as standard. If your PC doesn't have USB, USB cards are available but you would need to ensure you are running Windows 98 as well.
Ian