I was wondering how do I make a PSP UMD such as a game into an ISO that I can upload and link for others to download and play on their modded PSP's.

You need to use a UMD dumping program such as New UMD Dumper v0.2: http://www.psp-hacks.com/file/38
That one outputs the ISO to your memory stick, but I think there's another one which goes straight to hard disk through USB.
I think it was made by Booster by I don't remember the name of the application.

Alright, i'll try UMD Dumper.