For those who want to rip their DVDs to play as MP4s on their PSPs I can recommend "Xilisoft DVD to PSP Converter 4" as a simple solution (3 clicks or so) to do this. I've just converted 28 Days Later as a test and it took just over an hour - although this is on a dual core PC.
Just looking for one that does the same straight to AVI.
For conversion of videofiles like avi and flv I recommend the freeware 3GP converter. It is fast and its just drag and drop when you find your preferred preferences. Makes MP4 easy and reliable.