Couple o' things:
1) What's the resolution of these images? Make sure they are at 72 ppi, not 300.
2) How many colors are you using? In Photoshop, use the Save for Web function (5.5 and higher) and limit the colors in the palette. For GIFs, that means starting with Auto and working down to a handful, 2-10 colors, depending on the image. For JPGs, start witha medium resolution (in the thirties) and work down to the teens.
3) That 3-pixel high background image: how wide is it? A browser will tile the image, so you don't have to make it as wide as the page. Try 3 pixels high and maybe 20 or 40 pixels wide. (Note: too small a background graphic can make for real slow screen redraws.)
Keep working on it, it will come.