I agree with niefong. Danbooru is an image site; the best way to post doujinshi is to upload one or a few representative pages (ideally, ones that are interesting even when taken as stand-alone pictures), and post a link to the entire comic in the comments. The comic can be uploaded to rapidshare or similar services.
The exception to this are very short comics (eg a handful of pages), especially those posted by random artists on the web (as opposed to scans of actual doujinshi releases). There's no problem with posting these whole (assuming they satisfy the usual quality and content requirements, of course).
I don't think Fencedude's idea of embedding an archive inside a picture is a good one, for the following reasons:
1) it wastes space for people who archive pictures, who might not even be aware that there's a comic inside (especially if the pictures are posted elsewhere or kept in one's personal collection);
2) even if you remove the archive afterwards, you're still most likely to end up with a file that's different from the original (which breaks danbooru's hash-based dupe detection, and all sorts of other stuff that's important to people I know);
3) it wastes danbooru's storage and bandwidth;
4) it can cause problems with some browsers, especially if the archive is large.
Bottom line: better use rapidshare, megaupload, etc.
Finally, a word as a translator: although I don't think Almatia had bad intentions, it is a fact that by posting large comics you end up exploiting the work of the volunteers who do translations on this site (and diverting this limited "resource" from everyone else's pictures, too). If you're interested in having a whole comic translated, you should make a commission to a translator you trust. That will get you a better, more consistent result in less time, and it shows that you do appreciate the work involved in making a translation.
(If anyone wants to contact me about this, you can usually find me on the danbooru channel on irc.pyoko.org; wait there for a few hours if I'm sleeping.)