Starting with Windows Vista/Server 2008 the OS installer creates a BDEdrive volume of about 300 MB containing the boot files. This BDEdrive is necessary to use BitLocker.
If you encounter a shortage of space on the C-drive of a Windows Server 2008 server and you add extra space to the VMDK file containing the C-drive, you'll notice that you can't extend the C-drive with the added space beccause the BDEdrive is in the way.
If you are not planning to use BitLocker you can follow the following steps to extend the C-drive:
bcdboot c:\windows /s c:
Output when succesful:
Boot files successfully created.