Warning! Some information on this page is older than 5 years now. I keep it for reference, but it probably doesn't reflect my current knowledge and beliefs.
Sat 10 Oct2009
You don't have to use only drive letters C:, D:, E: and so on for subsequent disk partitions. Windows gives much freedom in managing drive letters and partitions, if you know how to do that.
First, you can change a drive letter for a hard disk partition or removable disk drive. For example, I like to have my DVD as drive X:. To do that:
Go to Start / Settings / Control Panel / Administrative Tools / Computer Management.
Navigate to Storage / Disk management.
Right click on a disk partition or DVD drive.
Select Change Drive Letter and Paths.
Use Change button to change drive letter.
Second, you can mount whole partition or drive in an existing, empty directory. To do that:
Go to Disk management as described above.
Right click on a disk partition or DVD drive.
Select Change Drive Letter and Paths.
Click Add button.
Select Mount in the following empty NTFS folder.
Enter a directory to mount the drive in.
And finally, you can do the opposite - mount a directory as a separate drive. The way to do it is quite different, as it requires to use a console command: