They keep telling me that my picture is too...

More information on exactly what you are trying to do would be helpful... But it sounds like it's a resolution problem. Computer monitors usually display 72 or 96 dpi (Dots Per Inch) Printers usually print out images at 300 or 600 dpi Some newspapers are printed at only 50 dpi Scanners can scan a photo in thousands of dpi...
If your photo is a 4x6 at 300dpi, then when they try to display it in 72dpi, it will display as just a bit larger than a 16x20" image
When you are scanning a photo to email, then make sure that you set your resolution to 72 dpi to display on the screen - or vice versa, if you are going to print something, make sure you scan it at 300dpi
If you have any graphic programs, (Microsoft offers "PowerToys" for Windows XP) you can open the file in that, and usually find a setting for the Image Size that will let you set a new DPI. It's usually ok to lower an image's dpi - but there is a loss of quality anytime you try to add dpi, since you are forcing the computer to "guess" what all those hundreds of dots should look like, and they aren't good at that.