The whole image sits a little to the right. I've seen an option in the NVidia control panel (or whatever they call it) that allows me to enlarge and do lot's of other stuff, but nothing as esoteric as Horiz. pos. ...Vert. pos neither.

Is there an xorg.conf setting I can tweak?

Nope. Nvidia's BLOB only offers a control to adjust the overall size of tvout (overscan). And if you have an 8x00 series GPU, you don't even get that much, the overscan control does absolutley nothing(!). I believe Windows users are complaining about the same thing and getting the excuse that it's down to Vista's DRM - it's been a long while since I bothered to investigate though, maybe my mind is manufacturing that explanation. The overscan control is definitely useless on 8x00 GPUs (and possibly later GPUs also, I don't know for sure) though. And there is definitely no existing option to adjust tvout position. Sorry.

I actually downgraded from my 8600GT to a cheapo 7200GS for a while because I was so fed up with not having an overscan control. Eventually I wanted a GPU worth a damn again though. Hooray for MPlayer's myriad command line options which can be used (in a maddeningly senseless manner) to shrink the fullscreen output so 1/4 of the picture isn't lost off the edges. Boo for the other options that appear to offer a position control in the manpage but don't actually do anything when you try them.

edit: the overscan option, if it works for you, is:

Option "TVOverScan" "0.7"

where 0 is the lowest and 1 is the highest. I believe it only recognizes one decimal place.