washed out in photo editors

Hi,

I'm a rank beginner, so please have mercy.

I have a couple slides I scanned that look fine in Windows Photo/Fax
Viewer (or whatever it is you get when you click on a .jpg in XP).
However, one of them looks totally washed out (like 5 shades lighter)
and streaky when I open it in a photo editor - I used Arcsoft and
Gimp. It's got a dark background, but I've tried others that also are
dark and they look OK in the editors.

Now, this particular slide is from a rock concert, Ektachrome 400
pushed to 800, so it's not your average snapshot. But how come it
looks OK in the standard MS viewer, even when I blow it way the heck
up??

And what's the picture **really** look like, if I ever get around to
putting it up on a Web site?

Thanks in advance,
Pat