Safe res for pic's in different user Resolutions

[caine]

I use clapsable tables to design sites, with a resolution of 1600 * 1200. But i always make sure that the design will happily clapse down to a width of 760 without looking too silly.

However, something that has come up due to me buying a new camera and remembering a criticism a couple of years ago about the sharpness of the Graphics of the pic's i employed around a site of concern, has drawn me to think what is a safe resolution that can bounce between width's of 760 and 1560 pixel's.

The new camera is a Fuji (lost the Canon in Boston), resolution of pics:

1. 640 * 480 would look terrible on a res above w = 1024,
2. 1280 * 960 the one i am tempted to go for!
3. 1600 * 1200 great for my eye's on my systems, terrible i fear for user's of the site with different rez's, and bad probably for ROI.

I'm not to hot on this so advice would be appreciated, as i have quite a lot of photo's to take over the coming weeks.

[netcommr]

can you make all 3 available through links, or a javascript resolution check then display appropriate image?