If you have Adobe PDF set up as a printer, you can select 'PostScript Custom Page Size' as your paper size. In the advanced document properties you can then edit the page size, not sure what the maximum size is, but when I'm designing reports to export to Excel I usually put the width up to 100 inches.
I realise this assumes that you have a full version of Adobe Acrobat. I'm not sure if there are any other 'virtual' printer drivers out there.
Edited by MaddMatt - 14 Mar 2008 at 6:01am