you can just assing the image a specific size with the image tag in HTML... just make sure to keep it the same ratio, should turn out fine...
The problem is that the entire image still has to load. Let's say you have a 1600x1200 image that's 400 KB. If you drop that directly into an HTML document & display it at 800x600, you still have to load the entire 400 KB to show the image. If you resize the file itself, you'd only have to load 100 KB to display the same 800x600 image.
Plus, I trust PhotoShop to re-size an image a lot more than I trust IE.
Viper GTS