ROM management: beginners lesson please

[craigiecraigie4]

Can someone please tell me what one can do to the ROM of a JJ, and how.
I expected to unlock, change file attributes, then move cab files across to SD and delete them from ROM to free up "Storage memory". Instead I unlocked (not sure what it actually did), changed attributes, then could delete but NOT copy cab files. Why can I not copy a cab file to my SD? I can confirm that deleting skype and backgammon cabs does free up storage memory. Perhaps I should just download a more recent skype install file from their website and then delete it? Guidance would be much appreciated...