After converting with ptf2rco, decompress the RCO with Resurssiklunssi.  That should be all you need to do.
Once you've done that, you can extract with any rco tool.  However, the extracted file you showed me appears to be still compressed, so you probably didn't put it through Resurssiklunssi?

Anyway, if, for some odd reason the above doesn't RLZ decompress the file, you can try doing it manually.  With the extracted background, open up an RCO containing icons.  Rename the extracted background to .dat  Replace the FIRST icon in the RCO with the .dat file.  Then open up the RCO in a hex editor, go to 0x11E and change the value there from 0x01 to 0x02.  Now run the RCO through Resurssiklunssi.
After that, open the RCO up, extract the first image as a .mig, and rename to .bmp.
Here is the output from the thing you gave me.