Any .htaccess/mod_rewrite Pros Out There?

I'm playing around with setting up a storytlr test server (Linux Mint "Helena", effectively Jaunty, with the usual LAMP stuff and avahi for ZEROCONF mDNS service) for debugging purposes here—posting notifications to Twitter is broken, broken, broken—and I wanted to put the installation in a sub-domain mapped to a sub-directory, e.g. http://live.karasu.local --> /var/www/live/. I'm running into issues trying to get mod_rewrite to do its magic.

You'd think there would be good examples of the right combination of RewriteCond's and RewriteRule's to accomplish this, and there may well be, but I'm mostly turning up more evidence that I'm not the only one who's had a lot of trouble with this, as well as a few things that seem, at first glance, plausible, but which fail disastrously in practice.

Anyone got a good canned solution for this? storytlr gets very unhappy if it doesn't believe it's in a top-level directory, and I'll just install it there if I don't come up with a better solution, but it's aggravating me that an (apparently) simple problem is so difficult to solve.

Oh, the following is for He-Knows-Who, He-Knows-Why: