|XP won't let you change the drive letter of the drive that has Windows on it, but you can copy the data on the partition or the entire partition to the other drive and reconfigure so that the copy on the 20 gb drive is C.|
The first consideration is what are you going to do with the 2gb of data that is presently on D:? If you can afford to lose it or can re-download it or re-install it you could wipe the D drive. If you need to save something on it, you need to have a place to copy it to, such as another hard drive, or Cds, or DVDs.
There are several ways you could cure your problem.
1. Copy the data onto a formatted partition.
One way is ....
You could get a drive prepartion utility from the maker of one of your hard drive brand's web sites, format the partition on D to wipe it, then copy the entire partition - it actually copies only the data contents in this case - of C to D with the utility (that is usually VERY slow because it thoroughly checks the data before and after it has been copied - verifies it).
After that, you remove the power to the case, and change the jumpers and data cable connections on the drives to suit the present D being the first hard drive and the new C, the present C drive being the second hard drive and the new D. E.g. if they are both on the same data cable, reverse the master and slave jumper settings on the drives to opposite of what they are now.
Disconnect the power connector to the 6gb drive before the first time you boot after that. The reason for doing that is if both drives are recognized, the 6gb drive will probably still be seen by XP as C, and the 20gb as D, even if you boot from the 20gb drive. Disconnecting the 6gb drive at first ensures the 20gb drive will be seen as C: by XP.
When you try booting the 20gb drive, it may not boot. It is easy to fix that situation.
With the bios boot order set to boot a CD before a hard drive (the best way to set that is floppy drive first, if you have one, cd drive second, hard drive third, if you can), insert the XP CD in a drive, boot the CD, when the initial Setup files have finished loading and you are asked (for the first time) whether you want to Repair Windows or Run Setup, press R. That takes you to a black screen and the Recovery Console. You will see a line for a Password. If there are no "stars" - asterisks - *'s - beside that line there is no password - just press Enter.
If there ARE *'s beside that line the password is the same one you used as Administrator for your original Windows installation on the original C.
At the prompt that appears
type: fixboot (press Enter)
type: fixmbr (press Enter)
type: exit (press Enter)
The computer will reboot automatically.
DO NOT boot the XP CD. Take it out, eventually.
The new C drive, the 20gb one, should boot fine.
Try Windows for a while to make sure everything is intact and working properly.
When you are sure that Windows is okay, remove the power to the case, connect the power connector to the 6gb drive, restore power. Boot the computer - the new 6gb D drive should be seen no problem. Go to Control Panel - Administrative Tools - Computer Management - Disk Management. Delete the patition on the 6gb drive, partition and format the drive.
You could also use a copying utility such as the freeware XXcopy to copy the data. They copy faster but usually do not check the data on the place the data is copied to as thuroughly - verify it - as the drive preparation utilities do.
2. Copy the partition to unallocated space.
One way of doing this is with a program package such as Partition Magic 8.x. On the CD is a folder \Rescue. If you run Setup in that folder it creates a 2 floppy set that has all you need on it to run the Dos version of Partition Magic from your floppy drive.
The floppy drive must be before the CD drive and hard drive in the boot order in your bios setup (the best way to set that is floppy drive first, cd drive second, hard drive third, if you can; a bootable floppy disk cannot boot on most computers if it is after the CD drive and before the hard drive).
Boot with the first floppy, insert the second one when prompted.
Delete the partition on the 20gb drive.
Check the partition on the 6gb drive for errors. If it finds errors, you will have to start up C normally and use Start - Run type: cmd, then type: chkdsk /f c: on your 6gb C drive.
Select the partition on the 6gb drive, and Copy the partition to the unallocated space on the 20gb drive. This is also SLOW, but probably not as slow as with a drive preparation utility copying the data.
When that is done, Re-size the partition on the 20gb drive so that it fills the drive, except I recommend you leave the last 8mb or the closest you can get under that, unallocated, as XP itself does by default.
Then proceed the same as starting at HERE: above.
If XP assigns a drive letter other than D to the 6gb drive because D was assigned to a CD drive, that can easily be fixed.
Go to Control Panel - Administrative Tools - Computer Management - Disk Management. change the drive letters of other than C to ones not yet assigned so that D becomes available, then assign D to the 6gb drive.