Here this is what I did to mine:
1) I got the download from the actual noobs site not here
2) Place everything on your psp, you better off using a fresh formated 32 but i used an unfress 1gb with 400mb left
3) With the HEN folder in PSP, all three save files in your SAVEDATA folder and the UPDATE folder in GAMES witht he 1.5 eboot renamed to UPDATE
4) Load Grand Theft Auto: LIBERTY City Stories, It has to be an early version (with a 2.0 update on it). If you bought it yesterday fat chance, but if you got it near release date you should be good.
5) Load GTA and the screen will flash blue and turn off, if not try again. When I did this I had less then 75% battery =P, I would wait till 75% and plug it into the wall.
6) Turn on the psp and check the system softwear. It should say 3.03 HEN. If it does go to step 7 if not go back to 5
7) OK now enter your memory stick as if you going to run homebrew and scroll down to find Update X.yz or something like that (red icon) and run it.
8) Your now 1.5! Now you can stay 1.5 or upgrade to 3.03 oe C.