MIRKOSOFT, do you already have the hardware needed?
PCMCIA flash can be rather costly
Why not use a USB device instead?
Hay not replace the HDD with a larger size? The price of laptop HDD has come down a lot. IMO, a new HDD is the best thing for an old laptop.
Amway, hate are many articles about how to do it.
Here is as simple method:
https://wiki.ubuntu.com/BootFromPCMCIAThis is for Linux Ubuntu.
Introduction
This Howto instructs you how to boot your root filesystem on a PCMCIA Flash Card (or a Compact Flash Card in a PCMCIA Adapter) after you've installed/copied Ubuntu onto the Flash Card.
Use of a PCMCIA may give poor performance.
You can find more information this way:
Google:
Boot From PCMCIA Some of the articles and not complete or useful because getting Windows to boot from other devices is not easy. But it is easy to do in Linux versions like Ubuntu.
Here it is with BARTPE
https://www.youtube.com/watch?v=szt97BSaHNUNotice how slow it is.
Watch the Ask Leo video that follows. He gives a general coverage of alternative boot methods. Using alternative boot devices is a security risk.