[CentOS] Delay during boot up

CentOS has recently started booting slower than it did before. Just when 
X starts up and the screen is dark blue and the only thing is the hour 
glass in the middle of screen turning round and round. It stays like 
that for quite a while, and then later it will resume the normal boot 
process. This long pause did not exist before.

This seems to have started happening after I installed a FAT32 drive. So 
my guess is that for whatever reason, it takes CentOS a while to mount 
that drive.
Actually, I'm a little concerned that maybe CentOS is doing something to 
the drive, some kind of directory reordering or something, because 
whenever I look at the drive from Windows and use Diskeeper 
(defragmenting software), it seems to have excessive fragmentation.

But I don't know for sure that linux is doing anything to the drive, and 
I don't even know for sure that it's because of the drive that the boot 
process now has this added delay.

So my first question, I suppose, is - What do I do to diagnose what is 
causing the delay in my boot process?

Dave