Well I was told that to get rid of fragmented files I had to reinstall OS X...I'm not sure if that's right or not. I have also read that I need to erase the entire internal drive, but wouldn't that render it useless? Can anyone walk through how to do this with me? Also, I was told that I would need to back up my drive to keep my files after the erase, but if I restored the drive using that disk image, wouldn't the fragmented files come back?
Also, when I plugged in my external hard drive (it's USB 2.0, with GUID Partition Table and Mac OS Extended (Journaled) Formatting), and open the Boot Camp Assistant, and press continue, it brings me right to the option of partitioning my internal hard drive, but there's no way to make it target my external hard drive. Any thoughts?
Thanks,
ARDesigns
WARNING: Read the following only after a couple of cups of strong coffee to keep you awake! Sorry!
OK, let's deal with the second question first (it's easier

). You cannot install Windows on an external drive because Windows is not designed to be booted from external drives- hence the BootCamp Assistant installer will not allow you to select your external drive as a valid destination. Boot Camp will only allow for internal drive selection- either your boot drive if a single drive system or any internal drive if you have multiple drives (as in Mac Pro).
I'm sure there are probably ways to hack it to work from external drives but I will leave that to others to fill you in on. I just stick with the standard Apple supported BootCamp usage.
Now the first part- there is a little confusion apparently in your idea of what fragmented files are, so will try to make sense of it for you as I
think you are confusing
fragmented with the term
corrupted.
NOTE: This is a
highly simplified version of fragmentation. Mac OSX has several internal routines to minimize the effect I am going to describe,
but it does not apply those routines to files over a certain size (most commonly reported as 20MB) so they can get scattered as in the example below.
When a file is written to the hard disk it is going to take up X number of sectors of the disk depending on its size. So, if you have three files (A, B and C and with x representing free sectors on your disk) that have been written to your disk one time they might appear like this on your disk:
AAAABBBBBBCCCxxxxxxxxxxxxx
Now the problem with fragmentation comes in when, using this example, you do some work on file B and increase its size. To store the additional data in file B when you resave it to disk, the OS looks for the next avaiable open sectors on the disk and saves the file in the original space plus the additional sectors. So assuming A and C have not changed, the new disk map might look like:
AAAABBBBBBCCCBBxxxxxxxxxx
And finally let's say first C and then A change but B does not- then the mess might look like:
AAAABBBBBBCCCBBCCCCCCAAxx
BUT- there is one more possibility which is what is affecting you. Let's say that file C is now deleted. The map will look like this- and the free space will no longer be consecutive- which Boot Camp needs the size of free space you have chosen for your BC partition to be:
AAAABBBBBBxxxBBxxxxxxAAxx
Anyhow, anytime a file is stored in two or more non-consecutive sections of the disk it is referred to as fragmented. Now think of the huge number of files on your hard drive and how often they are changed (especially system files in the background) and combine with large files that the system does not do an efficient job defragmenting and you can see the basic problem of fragmentation.
On the other hand, corruption refers to a file that is written to a disk and has an error in the write, rendering it unusable since the info contained is not what was intended to be there. Other ways a file can get corrupted is by shutting down the computer while files are still being written, and a program accidentally writing a file using some of an existing file's space on the drive.
Since there is nothing
wrong with a fragmented file per se, if you back it up and restore it it will no longer be fragmented since the restore file writes a single file at a time on a blank disk- so when
first restored each file will be consecutive on the disk and the example above on the restored disk would look like the following and all free space would be in one big block again- and the Boot Camp Assistant would be happy again:
AAAAAABBBBBBBBxxxxxxxxxxxx
Now backing up and restoring a
corrupted file will not change or fix anything- the file's corruption will be backed up as such and will be restored as a corrupted file, so no joy!
So, the simple answer to your question after a far too long answer is that one real way to regain the unfragmented space that BC requires is to backup the files on your OSX disk (with Carbon Copy Cloner, SuperDuper, Time Machine, etc.) reformat the disk and restore the backup. Or just reformat the disk and reinstall OSX if you have nothing you want to save (which I really doubt!

)
The second way is to use the commercial product
iDefrag, but without a full backup ahead of time for insurance, any program that moves files and rewrites them is a real gamble. If a program like iDefrag is partially through running and there is a power loss, etc. etc. etc. you could wind up with a disk that is unusable until reformatted with your data gone, so keep that in mind.