ezpkns retouching wrote:
Likely the unedited versions are just low-resolution previews. Retouching doesn't add size.

Of course cropping is not the answer, because you'll delete part of the image. You want to resize or resample. The terminology depends on the software used.

Let me know what software are you using to view your pictures, and maybe I can give you more specific help.

PS great avatar/look

Ah, thank you for correcting me!

Currently all I have is Windows Photo Gallery. Clearly not too useful, but I am shopping around for some better software.

Is it possible to resize using Windows, or should I wait until I get new software?

EDIT

Apparently I have Picasa2 as well.

ezpkns retouching wrote:
There are more specific instructions somewhere in the MM faq (about the maximum size before MM automatically resizes/compresses), but 750's a decent rule of thumb.

Yup.

From the Photography Forum FAQ

What can I do to make my images look good on ModelMayhem?

Start with a good original. 
Make a copy and resize it to no more than 800 pixels wide; anything larger will be resized by MM, and quality will be lost. (400x600 is a decent size, or 500x750.) If using Photoshop, Bicubic or Bicubic Sharper should be used for the interpolation method.
Convert the image to sRGB. (Photoshop: Edit > Convert to Profile, make sure Black Point Compensation is enabled)
Sharpen using your favorite method. (Unsharp Mask at 100, .4 pixel, Threshold 2 is a decent starting point for many images at this size if downsized using Bicubic.)
Save As… using JPEG filetype, and compression of 7-9 so that it’s under 500K in file size.
Upload to MM

That’s NOT the only way, but it’s one good sequence. If you use Photoshop, creating an Action to record these steps will save time, and help avoid missing steps.

For more information about the color issues, see the Color Calibration and Management Reference thread.

P.S. The DPI setting makes no difference. 72, 300, 1, 1000—it doesn’t matter for the web.

For the OP: There are online services such as ResizR (easiest for just resizing), Adobe Photoshop Express, Picasa (see above), Picnik, Pixenate, Splashup/Fauxto, Phixr, Snipshot and so on where you can resize your images using your browser if you don't have an image editor on your own computer.

Or the open source and free GIMP image processor, or...