When I got into photography I had the exact same point of view as you. I *thought* that I wanted to get into it but I wasn't sure if it would stick has a hobby so I didn't want to invest too much money in it. I bought a Canon PowerShot S5IS (the S5 is the predecessor to the current SX20 IS) and told myself that if I stuck with it for a year, I'd make the leap to a dSLR.
Looking back it worked out pretty well. The S5 took great shots and allowed me to learn some of the basic fundamentals of composition, lighting, etc while still being a small and portable camera. And it had all of the same modes that dSLR's have (AV, TV, Manual, etc). After a year I sold it on Craigslist and bought a 50D and I found that I was much less intimidated by it than I think I would have been had the 50 been my first camera.
One thing I'll add however is I've found that I still need a second camera so I carry a PowerShot S95. My 50D is gripped so it's pretty huge and heavy, and portability becomes an issue. The S95 is literally small enough to fit in my jeans pocket and it still has all of the same creative controls that the S5 had (and it shoots in RAW which my S5 didn't even do). My point is, after you get a dSLR you may discover that you need a 2nd camera anyway for when the dSLR is too big, so why not consider what would make a good backup camera now, and get that one with the intention of keeping it as a backup when you finally make the leap to dSLR. To that end, it would make sense to think about what brand dSLR you might end up with and buy a P&S now that's the same brand. It will make switching back and forth either since the controls and menu's will use common terms and icons.