Firstly, thanks to everyone who responded to my original enquiry - the
advice is greatly appreciated.

I have given switching power supplies a close look, and they are definitely
a much less crude solution than linear with huge heatsinks etc. I am just
worried about the switching noise, which should not be a problem for the PIC
part of the application or the part that requires the high current, but will
probably be a problem for a strain gauge amplifier (instrumentation
amplifier) I am using.  I have some questions to anyone who has experience
mixing low level analogue circuitry with switchers:

1. Can I use a separate 78lxx type regulator supplied straight from the main
24 V supply to supply the analogue part, and a switcher for the rest, or
will the switcher induced line noise on the power line still make my life a
misery?
2. If I use only the switcher, will I be able to get the supply clean enough
using RC low pass filters (bypass caps), or an LC notch filter, or will my
life become a still become a misery?
3. Any other advice/suggestions?

Thanks
Roland