You could always buy something like a
Butterfly Labs Japaleno, plug it in, and mine casually using something like
BitMinter.com...
But over time, you'll start noticing that downtime is kind of a bummer, that maybe you have to reboot it too often, it's hard to leave it alone to just sit there and mine, or it's running so well you'd like to try upgrading your setup...
Then you'll want to get a low-power host, running a light version of linux, and maybe setup something like cgminer, and have it automatically start mining when you boot and notify you when it goes down, so that you can squeeze every last bitcent out of your rig.
It's a slippery slope my friend. Soon, you'll end up being one of us.
Yeah, I guess that's what I was asking - can this be a "casual" activity. Didn't sound like that from a couple of responses, but I will try the suggestion about Butterfly Labs, which I had heard something about before, and that site, which I'm about to look through now.
I didn't intend to necessarily make it an individual pursuit, but BitMinter looks like a big pool, which would probably be more appropriate if anything. The concept I find to be exciting, as it certainly has a libertarian slant to it.