You would need to downgrade to 1.5 firmware first then upgrade to dark alex's custom firmware. That'll let you play the iso you have downloaded. Read up on it as much as youcan though, there are loads of guides and stuff on here showing you how to
If you PSP is firmware 3.00 from sony, You can't downgrade it. Don't try or you will brick your PSP. However, there are some guys out in those PSP retail shops that are able to downgrade it (hardware mod) but quite expensive.
You actually can downgrade your PSP without hardware-modding on it. There´s a new downgrader, fully compatible with all psp motherboards,
(CHECK HERE) but you need to upgrade to 3.03 first, an old copy of "GTA:Liberty city stories" (the new ones are patched to avoid downgrading), and enough patience to read all the docs before doing anything. If you´re a complete noob, i suggest you to get some friend who has done the downgrading procedure before. Remember, this modification leaves you without warranty over your PSP, if you mess it up, or something goes wrong, its all your responsability. Most of us have done this without a glitch, but you know, s**t happens.
From the lands of Maradona, Good Wines and even Better Women...
***// PSP1001 \\*** + 1GB Sandisk MS
1.52->2.00->1.5->2.71SE-A->2.71SE-B->2.71SE-C->3.02OE->3.03Rev.A->3.03Rev.B->3.03Rev.C
