(MONEY Magazine) – Steve Jobs just made me buy another iPod. And that ticks me off.

The moment that Apple's CEO announced the Mini, the slimmed-down, cheaper version of the company's popular digital music player, I knew I'd be among the first in line to buy one when they shipped in February. In fact, I placed an order as soon as I had a chance to play with a demo. Like the original iPod, the Mini packs a lot of power into a simple, clean package. Smaller than my wallet, the Mini has a 4GB hard drive that can store and play roughly 1,000 tunes. It has a more rugged design than its big brother and comes in five colors that aren't white.

But aesthetic appeal isn't the real reason I plunked down $250. I bought because I'm locked into Apple.

I was an early adopter of digital music. I've already spent $500 on a then top-of-the-line 30GB iPod, which I've loaded up with 4,500 songs, including at least $200 worth of stuff from Apple's 99¢-a-song online Music Store. The only complaint I've had about my iPod so far is its effect on my marriage: My wife and I keep arguing about who gets to use it. I decided a few months ago that the only solution was to get a second digital player. And since I didn't want to spend another $300 to $400, I looked at some players made by other companies. I found a few decent ones for under $100; most hold only 30 or so songs at a time, but that's plenty for jogging or a workout at the gym. Many are even smaller and lighter than the Mini. But for me, they're almost useless: They don't work with iTunes for Windows, the Apple software I use to manage my music collection. And, worse, non-Apple music players--that is, any player under $250--can't play all that music Apple sold me.

No one advertises this, but when you choose a digital music player, you're also choosing sides in a format war that reminds me of eight-track vs. cassette or Betamax vs. VHS. Any player can play MP3 files, the format most often used to convert CDs to digital form. It's when you start buying music online that things get tricky. Apple's Music Store sells songs in a format called AAC, wrapped in a copy-protection code called FairPlay. The only portable device that can play these files is the iPod. Most other online services, meanwhile, including the legal version of Napster and Wal-Mart's new service, sell songs in Microsoft's WMA format. WMA files play on devices from Creative, Dell, iRiver, Rio and Samsung (see below), but not on iPods.

Digital wasn't supposed to be this way. It's physically impossible to jam an eight-track tape into a cassette deck, but the only thing stopping the new formats and music players from working together is some computer code. The folks at Apple tell me, and I believe them, that it's a quality issue. If third parties were allowed into Apple's iPod/iTunes/Music Store world, it wouldn't be so easy to use. But Apple also admits that Music Store is, at best, a low-profit business--which suggests that the real point of its 99¢ songs is to get people to buy iPods to play them on. So don't expect this format fight to be resolved soon.

Which side should you choose? Go Apple and you'll own what's still the best-designed player on the market, working in tandem with the best combination of software and an online music catalogue. But you'll also pay more and have fewer choices. (Hey, longtime Mac users--ring a bell?) With WMA, your costs go down as your options go up. But you won't be as chic, and you may find that buying music and getting it to your player is a clunkier process.

That said, the gap between Apple and the competition is closing. The new Mini maintains the Apple advantage, but just barely. Memo to Mr. Jobs: Keep your techies working late to stay ahead of the curve. I've spent nearly a grand on your digital music revolution. If you make me regret it, you've lost a customer for life.