Step 1:you need a PSP ISO so get one somehow, if you have a CSO use the PSP ISO compressor like shown in this video to uncompress the CSO to ISO because it need to be an ISO or PBP file.
PSP ISO Compressor: http://www.mediafire.com/download.php?b1n7wk8en5vywy2
Step 2: Once you've got your ISO, mine in this video is GTA Vice City Stories, Open up the file ez_PSP2PS3_1.3.rar and extract the files and run the PSP2PS3.exe
Step 3: Click Browse and search for your ISO and select it, than just leave everything the same (checkboxes etc) and click Start and wait till the process is done.
Step 4: It will ask to check the files a couple times so just hit continue and allow the program do do its thing. When its finished, it will ask you to save the file as a PKG file, save it somewhere you will remember like X:\\Users\user\documents\PSPConvert
Step 5: Plug in a USB Flash Driver, (about 8GB) and open the root of this drive, Create a folder called Packages and then copy the new Created Package file into here.
Step 6; Unplug the USB and Plug it into your PS3, Scroll over to the game section and open Package manager and select install Package from Folder and you should see the ISO converted Package.
Step 7: Install it and wala PSP is now on PS3
NOTE: Not all work and there are some bugs known, if it does not work as PSp Remaster, try as a Mini, you might also need to use PS2 Classic with Multiman as well as PS2 Classic Manager Emulator to play the ISO sometimes too.