OhMyPixel - 11:04 pm on Jun 11, 2002 (gmt 0) <non expert opinion>I say PDF all the way.</non expert opinion>
Correct me if I am wrong BUT, I believe there are also scaling options in most browsers under FILE>PRINT. Not only will you have size conversion problems with the .GIF file but sometimes printers are set at 80% or so to make sure that web pages fit on the width of the paper. This could really throw off your graphic as well. It seems like this could create another problem if you are not careful - Being that this is something that your visitors are probably not going to be savvy enough to change (according to your post).
<non expert opinion>I say PDF all the way.</non expert opinion>