Allowing Windows XP with SP1 to recognize hard drive > 137 GB

I recently purchased and installed a Western Digital 160 GB Ultra-ATA hard drive for my Pentium 4 Gateway computer which uses the Windows XP Home Edition operating system. Prior to removing the old hard drive I did not have Service Pack 1 installed. I was aware that the SP1 upgrade was necessary for Windows XP to recognize hard drive space beyond 137 GB. I have now upgraded to SP1 and SP2. My question is what do I now do to access the remaining 23 GB on my hard drive? Do I need to reformat (I HOPE NOT)? Can I modify the partition to recognize the remaining 23 GB? Do I have to create another drive letter? Currently I have two hard drives (C: and D: - the 2nd one is 40GB and used for storing digital photos, music, etc.), two DVD+RW drives (E: and F and a floppy drive (A. If I create another drive with the remaining disk space will the driver letter be G: or will the DVD+RW drives change to F: and G: so that the new hard drive becomes E:? Obviously, I would like to minimize the number of drive letters if possible.