PS2 widescreen mode: doesn't fill HDTV screen completely  

It's game dependent. The developers tend to make the viewable picture smaller to compensate for most TV's overscan, so the picture doesn't always fill the screen. I wouldn't bother trying to fix your TV as the position and size of the picture changes with every game. The best you can do is go into the Options menu of the game and try to adjust the X or Y position of the screen and center it.

I've noticed that as well, Metagroboliser. I have a PS2+component+Pioneer 4340HD Plasma and I do notice thin vertical bars at both ends of the display. All 20 games I've tried give similar results. I don't notice this on xbox games though. I guess it's the PS2.

Yep, but for the record I have seen it on some XBox games too.

Yeah, the PS2 output makes allowance for major overscan. 10% in all directions! I only found out when I upgraded my system to one with no overscan. Fortunately, I can zoom the image to fill the screen.

I have seen it for Xbox games, the vertical bars are not always even either.....it really does suck.

I've seen this on both my PS2 and gamecube.

I've seen it on every system that I own, from the NES all the way up to the Xbox.