You can resize your photos directly on ImageShack, but you will have to make sure that the weight is correct beforehand. You can use a programme like Photoshop to do that.
Go to the ImageShack site and click on "browse" to upload your photo from your hard disk.
Tick the box marked "resize image" and choose the 640 x480 format for message boards in the adjacent menu.
Then proceed as indicated in the section "How to host a picture..."
Just in case you're interested here's a nice freeware to do slideshows with your pictures :
http://picasa.google.com/
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