My standard is 4x6" at 72 DPI and usually about a "65" (out of 100%) on the jpg compression.  This yields a decent compromise between view-ability and size.  I shoot for file sizes of 20-30k just so I can upload them effectively on my back-woods dial up connection.  The forum does have some automatic compression that will come into play if you post huge files.  You DON'T want that to take over as it tries to do it all with jpg compression, resulting in badly pixelated images that are still physically large in corner-to-corner dimension (worst of both worlds).

Not all photo editing software gives you the control needed to do the above, and LOTS of cameras don't.  But the easiest way might be to start by using your camera's resolution control to select the LOWEST possible resolution when you take the pix.  If you can get down to something that's near 640x480, or 720x540 (DV std) it'll display nicely here.

There's no need for "megapixels" when the goal is web presentation.  All of my G-tech article pictures are taken with an old Kodak camera that's only maybe 600k pixels total.

You can run a little experiment for yourself.  Take the same picture 3 tiems with your camera on different resolution settings (some cameras don't give numbers but when given choices like "fine" and "coarse" go for the latter - don't worry, the "worst" possibel picture your camera can take will look fine here) and then upload all three to a test message to see the effects.  Maybe you can get it all done satisfactorily in the camera.  When you have your answer, go back and delete your test post in order not to chew up server space with it.

All the best,

-Dave G.

PS- I REALLY appreciate your asking the question, as well as the little tutorial Dutch posted here a while back in response to a similar question from AMZ.  When I access from home, like now, monster pix take for ever to load, and sometimes I dont get them at all.  It's nice that this forum also liss them as attachments so that when the pix don't come across in the message, I can still click on the attachment link and get the pix individually.  I had to do that today with the pix Bill posted of the lamps.  That thread had so many pix, and some of them huge, that my connection gagged somewhere half way down and in order to see the pix in the last post, I had to download them manually.  I'm glad I had tht option.

Anyway, Thanks for asking!