Shouldn't be that difficult really, but it is going to chew a lot of screen height. As long as you don't mind that.
Oh, it can be done but put it this way. With the images involved in this particular theme it would be more work than expected. The head-l.gif and head-l.gif images blend somewhat with the bdy-tl.gif and bdy-tr.gif images. To get a seamless static header area it would take more work than simply altering css as with most other themes.
I am thinking at minimum, the bottom of the head-l.gif and head-l.gif images would need some doctoring along with some sort of added bottom border for #bnr to give it a finished look as opposed to just cutting off the head-l.gif and head-l.gif images at the bottom and calling it a day.
But, since it's not that difficult, go for it.