Hello!
If I were you, I'd take the time to do a sample dredd script, rather than just sending something you've already done - UNLESS the something you've already done has been published by a major publisher already and you just want to let 2000AD know that you exist.
If may take a few months before the Mighty Tharg gets to your submission in the pile (or a lot longer) so it's not going to speed up your chances a great deal if you take a couple of weeks to put together a brand new submission.
Don't forget, you're not just letting 2000AD know that a) you exist, b) you can draw but also that c) you can take on a professional attitude and draw what's asked of you - and the only way to prove that is to do a script that Matt has seen drawn by other people - ie, a sample script.
If you send him an AMAZING, drop dead awesome sample, the chances are he'll probably ask you to do a Dredd sample ANYWAY as a way to ensure that you can actually draw from other people's scripts.
As regards to size/format - first never send anything but photocopies, secondly, don't worry too much about size - as long as the samples fit onto an A4 page - this will never be published and, if Matt likes what he sees he will send you the full, proper specs (or, if you want, measure an issue of 2000AD and multiple all sizes by 40%)
Re: samples - make sure your contact details are on every page, number the pages and put the name of the story on each page (ie, "J.Smith (
jsmith@jmsith.com) Sample Dredd Page 1 of 5")
Include a cover letter that should be no more than a page, introducing yourself, describing any published history you have and thanking them for their time in looking over the samples.
Include a stamped self addressed envelope (for feedback and the return of your artwork).
And, finally, don't hold your breath, 2000AD have a LOT of other things to do as well as look at samples. Get a portfolio together, send it to:
FutureQuake (no money, but they have a bunch of titles and can always use an artist and they're a good bunch of lads/lasses)
Insomnia (no money, but they're really pushing the books they do and they look pretty damn nice and are doing lots of original graphic novels)
And... there's probably a load more.
-pj