adding new module position outside the right margin of the template

if i wanted to add a new module position outside the right margin of the template how would i do this... thinking about adding some banners down the right hand side of the site... ( this would be outside the template wrapper )

dimensions would be roughly 150w x 400h... is this possible and what would i need to edit... if not can anyone recommendan extension to download and use in lieau of this...

trey