if you have windows just right click on image file and select open with microsoft office picture manger or open with office 2010. from there you can adjust the image size, I usually use one of the pre-defined sizes and pick "web large".

Of course, now that you have the photos uploaded to photobucket at a decent size you could just ricght click on the image from your web browser and save it, then re-upload to image forum.

-David