I do quite something with photography, and when saving it i mostly deal with quite some quality loss.

I edit a NEF/PSD file, and when i save it to a jpg, it loses alot of color, contrast ect.
(Saving it on 100% quality doesnt matter.)

When i open that saved .jpg file, and i start editing and save it again, it doesnt lose any quilty.

Now i know that there are quite some jpg files around that have extreem high quality.

How do they do it!? and how do you guys deal with this? going to png files is an alternative, but this also seems to get messy. Any special settings that im overlooking? or maybe another aplications besides cs2?

post exampls (screenshots,- closeups) of what you mean in particular. You can also save as PNG which allows you to save as 24bit (3x 8bit RGB channel) without quality loss while still compressing to some extend.
Other formats such as JPEG2000 are very rare though very advanced because of the license policy some idiots started.
I know that microsoft started a custom HD format (dont know the extention anymore) that should come with VIsta that is very advanced regarding image compression while keeping amazing quality.

Rens: that's because jpeg uses a lossy compression algorithm in which you lose some details, even at 100% setting.

Just go with PNG or another lossless image format