It just doesn't exist guys, sorry. I'm assuming you already know that GarageBand is owned by Apple well this presents a bit of a problem for Windows 7 users. Apple and Microsoft are direct competitors and Apple doesn't exist to make Windows users happy. In fact they want you to move over to Mac if you want to play with toys like GarageBand.
In fact do you remember the adverts Apple ran saying Windows computers were for boring work and if you wanted to do the fun creative stuff then you needed a Mac?
Now don't go running to buy a Mac. Just stop and sit right back down.
It was a marketing campaing from Apple and nothing more. Most of the work I do - I do straight from Windows 7 and do you want to know how? No, I don't have some magic voodoo secret for getting GarageBand for Windows. No, I don't dress a Mac up and pretend it's a PC. Here's the hint guys: I don't use GarageBand.
Really? Next to nothing. Apple has always had a flare for dressing things up in a pretty box. Their software has the sleek look of top of the line music production but the look is all it has. GarageBand is really just meant for peopel to mess around with and get bored. It misses a lot of the functionality that even the lower end alternatives have. You do miss out on some of the 'learn to play instruments' vidoes Apple gives you but I think they'd just like you to pretend YouTube doesn't exist.
And just a bit of blatent self promotion here not only do I have a bunch of videos on YouTube but we have video guides on using the alternatives properly so you don't even miss that. All you're missing is the little apple logo and the hefty price tag for an Apple computer. And you gain the extra functionality and the ability to stay with an operating system that can run pretty much everything else. Personally I would say that is a pretty good trade.
I don't need an Apple logo on my screen to make beats. In fact here is a video I made proving a point about making music with Windows and everything on it - you can do straight from Windows 7. In fact there are several tools which run on both Mac and Windows.
I know GarageBand is a pretty fun toy but digital music creation extends a little outside the range of realm of Apple. I've seen dozens of different tools and there is probably hundreds out there. So while I can't give you a way to get Windows 7 running GarageBand (I've even tried emulation and trust me it so doesn't work) I can certainly give you some suggestions.
Actually I can narrow it down to one suggestion: Understand that GarageBand is only one tool. There are plenty of alternatives and some of them are actually much better than GarageBand. So all you need to is pick one which actually works for Windows. You can check out our download page for working Windows tools but you should also consider our (free) training. Rather than just give you some great tools and leave you lost on how to use them I'd like to actually teach you. If for no other reason than I get to stick it to my Mac friends when more Windows users are making sick beats.