Hopefully will cleare a few things up (just read the bits in bold if you don't care about my babbling!):
Resolution : pixels x and y, e.g. 2592 x 1944. Good for printing, pointless for on screen viewing. Most monitors are 1240x1024.
You said you were trying to get your images to VGA, VGA is 640x480 resolution, personally
I would resize them to 800x600. (SVGA)If people then want a larger version for printing and whatnot, they will have to ask for it.
Dimensions : means nothing to me...
Ratio : which is what I at first thought you meant by dimensions, is obviously the ratio of height vs width. When resizing, keep this the same and the image will look good in almost any size.
As most monitors are 1240x1024 they cannot display any image above this resolution at any greater detail. Any increase in resolution / filesize above this will be lost (not lost, but won't be represented
)
A monitor at 1240x1024 is about 1.3MP, so MOST of you 6MP image is not shown. You could do an experiment, resize the image to the maximum size of you monitor and view that and the original, they won't look any different, now if you were to print them at the same size (lets say full page A4) they would look very different. Printing has a much higher resolution than screens do (it's called dpi in printing though) and you can change the dpi in printing, you can't with screens.
You can compress .jpg images but increases the fuzziness / blurriness if done too much. You will not save that much space by doing this but will lose quality if you go too far.
There is no point putting a .jpg in a .zip file, it will not compress it at all and may actually end up slightly bigger. .jpg is already compressed and the zip algorithms won't help.
I personally use photoshop to do all this.
If you want a free, good package, I recommend GIMP for windows http://gimp-win.sourceforge.net/stable.html It has its fame/roots from Linux.
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