Changing the driver letter path and the letter did not change from windows XP to Windows Vista. If you are using large external hard drives USB memory sticks this will be handy. Sometimes when you connect hard drives to computers it get confuse and unable to display the driver letter.
Steps to add change the driver letter
(You can follow the same steps in Windows Vista and XP)
Go to Control Panel
Go to Administrative Tools
Go to Computer Management
Select Disk Management under Storage
It will show all the hard drive partitions and external Hard Drives. If it had problems assigning a letter you can manually give one by right click on the partition and by selecting
"Driver Letter and Path"
It will give options to Add, Change or Remove a driver letter. It is actually manually mounting hard drive in Windows.