I find resizing them to 640x480 or 800x600 makes a nice posting size. Download and use the excellent free picture program Irfanview. Use irfanview to resize to the above sizes - Image tab - Resize, then go to the File tab - Save as - name the pic and put it somewhere you can find it on your hard drive. Sign up with photobucket and upload your resized pics. Copy the IMG url below the pictures in photobucket for each pic and just past it in the text of the post.
Photobucket now uploads any size picture and has easy resizing options from within the website.
Let me know if you need any help.