PSX/PSOne/PS1, whatever you wanna call it, now play ‘em all with Popsloader — the full-fledged PSOne emulator — for Custom Firmware 5.50 GEN-A. How? Here’s how:

1. Download Popsloader below, extract it, and copy the contents to seplugins on your memory stick;
2. Create a POPS.txt file under the seplugins directory and add this line to it “ms0:/SEPLUGINS/popsloader.prx” (without the quotes);
3. Download Psardumper;
4. Download the 4.01 firmware eboot;
5. Extract the 4.01 firmware archive and copy EBOOT.PBP to the root of your memory stick;
6. Using Psardumper, dump and decrypt 4.01;
7. Copy ms0:/F0/kd/impose.prx to the seplugins/popsloader directory;
8. Depending on the firmware version you wish to use (see the above screenshot), download the corresponding firmware eboot here;
9. Again, decrypt that firmware eboot using Psardumper;
10. Rename the following:
    • 3.00 – 3.03: pops.prx, popsman.prx, meaudio.prx, pafmini.prx
    • 3.10 – 3.30: pops.prx, popsman.prx, pafmini.prx
    • 3.40 – 4.01: pops.prx, popsman.prx, pafmini.prx, libpspvmc.prx

    to popsXXX.prx, popsmanXXX.prx (XXX being the firmware version, ie. pops310.prx), and so forth for each file;

11. Copy the new renamed files to the ms0:/seplugins/popsloader directory;
12. Enable Popsloader via the recovery console;
13. Copy your PSOne game eboot to your GAME folder and enjoy!

Download:
Popsloader for CFW 5.50 GEN-A
Custom Firmware 5.50 GEN-A
PSP Firmware (EBOOT) Updates

- source: pspgen