Forums | MacLife

I'd backup, reformat.

If you haven't solved this yet and/or seen this nearby, Gizmodo's info likely covers you.

..
Boot Camp, and the process of installing Windows in most cases, couldn't be more straightforward, at least as far as operating system installs usually go. After you've got your Mac up and running like normal, fire up an app called Boot Camp Assistant (just use Spotlight). It'll warn you to back up your disk before installing Windows, which you should, since you are asking favors of the hard drive gods here.

Boot Camp Assistant will ask how much of your hard drive you wanna dedicate to Windows. You want more than the laughably small 5GB of space it suggests. Since I keep around 3-4 games on my Windows partition at a time, and I want some breathing room just in case, I stick with 40GB, but you probably really want no less than 20GB. Slide the bar toward the Finder face, granting Windows how much hard drive space you want it to have. After you click partition, Boot Camp Assistant will start getting your hard drive divvied up for some Windows action, which'll take a few minutes. Once that's done, you'll need your Windows disk.

If everything went according to plan, skip this next section!

If something went wrong
It's possible you'll get an error that says Boot Camp Assistant wasn't able to create the partition because some files couldn't be moved, and you need to format the drive into a single partition. Basically, what's happened here, most likely, is that your hard drive is fragmented like a mofo, and there's not enough contiguous space for Boot Camp Assistant to create the Windows partition. Yeah, disk fragmentation. In OS X. Believe it. From here, there a couple possible solutions.

If you're extraordinarily lucky, it's possible you might be able to simply restart your computer and stuff will just work. Probably not! From there, you proceed to the free and easy solution. Using Disk Utility, resize your main OS X partition, reducing it by 40GB (or however much you plan on making your Windows partition). Hit apply, and pray. If that goes peachy, you'll have 40GB of unused space on your disk. Go back to Disk Utility, and re-expand your OS X partition to reclaim the 40GB. After that's all done, run Boot Camp Assistant again, and since the hard work of moving files around on the disk was done by Disk Utility, you should be golden.

If, on the other hand, Disk Utility also refused to change your drive's partitions, you have two choices. The nuclear option is to back up, format your hard drive completely, then run Boot Camp and divide your hard drive into partitions from the Snow Leopard installation before restoring all of your OS X data via machine. Since my Snow Leopard install was practically virginal, as a totally clean (not restored) install that was only around 10 days old [ed. note—how the hell did your hard drive get so fragmented then?], I said screw that. Which led me to iDefrag.

How to Survive Boot Camp (and Run Win 7 on a Mac)