Don't use photobucket for resizing pics. They never quite turn out right. The resize feature in photobucket is merely concerned with file size so that you aren't taking up too much space on their server with your photo albums.
There is an easier way....
If you guys were to open your pictures using Microsoft Photo Editor, Adobe Photoshop, or some other similar photo editing software you will be able to resize them and then upload to photobucket.
Just look at the menu options on the title bar and look for something that tells you Image or Image Size. Sometimes this feature is found under a Tools menu or under Edit or Read the dimensions in pixels not percentage. You can change back and forth by clicking on the drop down menus next to each dimension.
To resize, just change the width dimension to 400 pixels. This will tell the software to resize the picture proportionatly to the dimension you have requested for the width. The length isn't as important for posting in a message so don't worry if it is a shade over 600 pixels.
Then upload to photobucket and post like you normally would. The size should be perfect!
For an avatar pic...
Go through the same process, but when you see what the original dimensions are, change the largest of the two (width or length) to 120 pixels. This will automatically resize so that the picture is the appropriate size for an avatar!
Make sense? Let me know if you didn't follow that...