I have created buttons using javascript. is there any way to write code so that i can change the shape of the butoons from the normal rectangle to other shapes such as a circle.
No.
You can use an image and an onclick image switch to achieve the same effect.
i think i saw a triangle one around somewhere lol...
Twey is right though, all you really need is to make your button image anyway you want, and if your adding a link, it'll just go around the corners a little...