The problem is the quality and EXIF data all bump the file size up.
Follow the good instructions above to get the longest size to 800 pixels, this will lower the file size from the original but may not be low enough to post your picture in the gallery.
If the file isn't small enough try the 'Save for Web' option under the File menu. This will strip the EXIF data. If the file size still isn't small enough you'll have to play with the image quality slider in the Save For Web options. Keep decreasing the image quality until the file size is just under the 200k limit.
HTH
Mark F