make sure you set the units select list to pixels next to where you enter the number, by default the units select list will be left empty, you need to manually set it to pixels.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.