i just downgraded my psp fw from 3.03 to 1.50 and im not sure what the next step is. do I have to upgrade to custom fw to play iso, cso and dax. and what fw should i upgrade to

I was just in a similar situation--here is what I did.

1. Updated from firmware 2.6 (this is the firmware my PSP came with) to 2.71.

2. Downgraded to 1.5.

3. Updated from 1.5 to Dark_AleX 3.10 OE-A.

Once 3.10 OE-A was installed I formatted my memory stick. In the root of the memory stick there is a folder called ISO. I just dropped a couple of .CSO files in there and it worked just fine.

If you don't want to update to 3.10 OE-A, I'm still pretty sure you can run .ISO and .CSO files--but I don't know how. All the research I did said that 3.10 OE-A has all the benefits of both 1.5 and all updates through 3.10. Most of those guides also recommended the update to 3.10 OE-A because it add a lot of functionality past 1.5.

I just followed the step-by-step instructions and everything worked just fine.

Just to elaberate a little on what Reverendrun said.

You only need to read the parts on updating to 3.10OE-A

Once on there you should have a folder in the main bit of you memory stick called ISO

All the games (.ISO or .CSO) go in that folder then if you go on your PSP's menu and go to Game then you will see the games