This should work on 1.50 firmwares, and all custom firmwares.
I Tested this on 3.10 OE-A2 and didn't enconter any problems
1.) Download "USB Special System Storage":
USBSSS_100.rar [40.2 Kb]
2.) Extract it using "WinRAR"
3.) Open the folder you extracted from "WinRAR". (USBSSS_100)
4.) Go into folder "MS_ROOT"
5.) Copy the folder "PSP" to the ROOT of your PSP MEMORY STICK. (eg. X) - (X as in the drive letter of your PSP) - (Click on overwrite, it will only add extra files and folders)
7.) Then on your PSP goto "GAME" -> "Memory Stick" -> and start "USB Special System Storage"
9.) Select the first option; "Virtual FAT16 . UMD ISO-9000".
10.) Now go to "My Computer" and open up the PSP drive. Where you should see your game. in ISO format
12.) The back-up process should now start ( the back-up will be finished when the percentage on the PSP has reached 0% again )
If the back-up gets to 100% and doesnt go back to 0 after 5 or 10 minutes procede to step 13. This has happened to me on several occasions but has still produced the full ISO image
13.) Press "X" to disconnect.
14.) Choose "Exit to XMB"
15.) Rename the copied ISO file pn your PC to anything you want and your all done
Guide: How to Downgrade/Upgrade Your PSP and Play Backups
And finally please DO NOT pm me with questions about this guide or software post your question here and i or other users will try and help you