Do you use Photoshop?
It has a wonderful tool called the "Single Row Marquee Tool"
You make the fade you want in any art program and then in Photoshop you select the "Single Row Marquee Tool" and click on the fade. The tool will select a one pixel row either horizontally or vertically which you can then save as a tiny file and use in a cell or a table on your webpage.
When you use this tiny file as a background in a cell or table, it will propagate to fill the area of the cell or table. You get a totally seamless fade!
The fades in this page
http://www.artofendeavor.com/ are single row propagations
Hope this helps
Cheers
Bodhi