i'm a little bit new at the whole modding situation but i have a idea for the internal hardrive situation. i understand that there have been alot of blocks and difficulties and that some poeple even think it's impossible.
what if you were to take the memory stick and dissasemble it(while first figuring out what does what) and wire it to an ipod hard drive with a piece of the ipod circut board but kill everything but the harddrive and the battery for the power source(headphone jack screenetc.) and even leave the chargeing port, just cut a hole in the back of the psp to access it to charge the hard drive battery. while wireing the two together get rid of the block that tells the stick how much memory is on it and pass it on to the hard drive. that would take care of the hard drive part now the internal part.
remove the umd reader, set the hardrive in the back and cut a hole in the door for the ipod hard drive chargeing port(make the circut board as small as possible to fit) plug the wired memory stick internally, seal the stick door and put it together.
this is just and idea if you think it won't work please tell me or if there are any questions about anything i might have left out, sorry if it's confusing i put it down as well as i could... i'l draw up plans and all that