Well there are ways to get GarageBand installed on a PC, but they involve degrees from MIT to get it up and running, which pretty much negates the simple to use/does what it says on the box vibe. Luckily for you some pretty smart software engineers have recognized the appeal of GarageBand and have implemented its goodness into software for the PC.
There are a few, but by far the closest implementation is Mixcraft from Acoustica, so much so that it has already earned the nickname GarageBand for Windows in DAW circles. Of course it can’t be 100% identical for copyright reasons, but with just a few function name changes and a slightly different design it is as close as you can get without ending up in patent court!
So, while it is easy to use Mixcraft as a musical notepad, when you need a little bit more meat with your potatoes then you aren’t stuck with buying more software to handle it. With GarageBand you need to buy Logic Pro to complete the full DAW experience. Mixcraft also works with all the VST plugins that the elder statesmen of DAWs run. If you think you might need more in the beginning, it’s probably a better idea to by Mixcraft Pro as it comes with many extra plugins including mastering plugins (Ozone from isotope and industry standard) and some really cool virtual instruments like Acoustica’s own Pianissimo (a really cool grand piano) or their implementation of the Moog.