wow, thats quite a big banner there. If the banner is gonna be advertised in your own site, than of course the sky's the limit. A guideline of sorts does exists for banner sizes. Its good to conform to it if you or your fren decides to use the same banner to be advertised on other sites.
with regards to the software, easiest i can think of right now would be photoshop templates. But if you're after a non-static banner, then you might need to bring those assets you've just made into another software