First, just to be sure: you did install texmaker via the software center right? If I got it right, you're coming form Windows world, and an habit to change in Ubuntu is the google/download/install cycle.
I've noticed that ps2pdf does not work because ps2pdf in ghostscript uses bat files for processing, most likely due to PATH not being what it should. I suggest using a bat file to start texmaker which temporarily changes PATH to include miktex-portable/miktex/bin, and restore on exit, such that the ps2pdf utilities do not run into issues. This also simplifies the texmaker path settings. The path variable change will only effect the command line instance that it is changed in, and not system wide.
Sorry, I don't use greybird, so I didn't recognize what toolkit that would be for. XFCE uses gtk, but texmaker uses qt. This is why the theme(s) you select for xfce have not been (fully) applied to texmaker.
I'm considering your suggestion to reinstall entire system, because I'm having strange problems also with installing emacs and texstudio, and this things have never happened before. Aside of this considerations, your last suggestion DID IT, texmaker it's working now! Thanks a lot for suggestions and time you've dedicated to me! Best regards!
Feed it the appropriate prefix (in our case /usr/local/shared/suse-11.1/texmaker/1.8). You don't need to be root for most of it despite what the instructions say; you just need to do the last 'make install' stage as root.
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