You can shrink pictures (well, JPGs at any rate, and all cameras can output JPGs) using MS Paint, which comes free with every copy of Windows. Use Image...Stretch/skew... Remember to shrink horizontal and vertical by the same amount (most other drawing tools have a lock aspect ratio option). I agree, best to shrink all images to about 640 wide. Height doesn't matter so much.
Videos? I'm not sure about this, but if you embed a Flash it doesn't actually animate on first opening the thread, does it? You have to click on it first. So bandwidth shouldn't be an issue if you don't actually view the clip. Personally, I have no problem with people just posting a URL to the relevant item on Youtube or whatever...