first method... assuming you have a way to import footage directly from a DVD... get a standalone DVD recorder. Output the ps3 to it, or split the signal to both it and your regular TV ... It'll record the dvd with your gameplay footage on it, and then you can put the DVD in your computer and import the footage... either with a video editor that can pull from DVD, or else a program that can record from a dvd as it plays on your system.. The first choice there will be the better option.
Next method, get a video capture device. Pinnacle makes a couple nice ones, I believe are called studio moviebox. You can get a USB version (external) and a PCI version (Internal) ... it'll let you capture footage as you play the games as well, and it saves a video file after you finish capturing, which you can put to youtube as well.