I suggest making a folder tree first where u have a folder for BEATS and then one for SOUNDS. File management is just as important on the mpc as it is on the computer when making music.
Inside the BEATS folder make another folder for each beat with whatever name u choose. Then when u go to save, choose SAVE ENTIRE MEMORY and put it in that new folder u made inside yer beat folder.
Name the PROJECT file either sequentialy or something your sure to remember so that its easier to calculate how far your going back when u open each new project.
(I often just call the first one 01 and then the next 02, and so on.)
Also, anytime u save a new project file to that folder and u have made any kind of alterations to the sample content in that song you should choose to REPLACE SAME SAMPLES...This will ensure that u have updated the files for when u reopen it.
*A last tip is: In order to save file space on your internal harddrive or FlashCard - Make sure to PURGE all files in the PRGM window that arent being used anymore after chopping to ensure that your not saving useless files that are taking up precious space on your media.
Hope that helps.
STEEZ