Where can I find a software that opens a file *.pxm with the header
FOR4?
I've already tried to open it using standard portable pixmap softwares
including Able Graphics Managers and standard convertors.

zaverijay...

A .pxm file is Pixel Magician native format : Bitmap graphics.
ACDSee ought to be able to open it - you can add the extension
manually, under Options -> Miscellaneous -> Set File Associations.

They have a trial version you can test for free:
http://www.acdsystems.com/English/Products/ACDSee/ACDSee-Download.htm

sublime1-ga

ACDSee does not support .pxm - at least the ACDSee 5.0 User Manual has
no listed support for .pxm files.. Even if I create an association it
does not work - neither does renaming (a copy of) my files to PPM/PBM
etc. or some other format.. Do you know of a plug-in for ACDSee that
supports .pxm format? Alternatively do you know what software created
the FOR4 header on the file?

I'll second that ACDSee doesn't support .pxm. I have ACDSee 5.0
installed locally and I've checked the file associations. It isn't
there.

However, Able Graphics Manager should do the job.

Graphic Region - Able Graphics Manager
http://www.graphicregion.com/products.htm

It claims here to be able to both input and output PXM files.

Are you using an older version of this software. Also, could the file
you're trying to open be corrupted?

zaverijay...

I only find one reference to the FOR4 header. It shows up
in a page whose root seems to have to do with computer-aided
architectural drafting software (CAAD). It speaks of a program
called MAYA which utilizes an IFF format to generate images 
within programs. The use of FOR4 in the header is mentioned at
the bottom of this page:

"FOR4 group of type TBMP (tiled bitmap)"
http://caad.arch.ethz.ch/info/maya/manual/FileFormats/ImageFiles.fm.html#9978

...and on this related page:
http://caad.arch.ethz.ch/info/maya/manual/FileFormats/IFFmanPages/ILintro.html

Maya 2.0 is 3-D Modeling Software:
http://www.npaci.edu/online/v3.19/maya.html

...available from Alias:
http://www.alias.com/eng/products-services/maya/

If your image was created by MAYA, I doubt any normal
image viewer will be of any use.

sublime1-ga

Thank you for your comments: 

I've got Able Graphics Manager (ver 2.2) - downloaded a few days back
from their site - it gives an error while opening this file..

The file is definitely not corrupt - there are over 15 files and when
I open them they look structurally intact with some words at the top
that I recognise to be in the file and the rest in hex code..

I've not tried Maya - I'll try and get back.. Thank you again for your
help.. Are you all not the 'official' researchers?

Jay.