Hoping you're still around, wm-cheng. Did you settle on a good way of doing this? It seems to me that whether a DVD is ripped to an ISO or exists inside a VIDEO_TS folder, you still only get to play each VOB file individually. That is, you have to sort through on the ps3 to find the biggest one, and that's hopefully the main feature, which is a bit of a pain.
I used Mac The Ripper to rip just the main feature to a single VOB, and that does work. It's just a file on the PS3. Won't play natively though, only if you pick it through a transcode folder. Interestingly, if you use Handbrake to rip to an mkv file, and then use an app like mkv2vob, that single vob does play without transcoding. Love to know why this is! Maybe it has something to do with the fact that the converted mkv file is only 1 or 2Gb, whereas the directly ripped vob is in excess of 4Gb.