Currently I am using one of my XP Machines and so will describe the process for XP. When I get chance I will check one of my Vista Machines to see if the process is the same.
Step 1.
Step 2.
Step 3.
Repeat for your other hard drives but set different days of the week so that one hard drive per night gets de fragmented.
In Step 3 above.
To defrag drive c:
C:\WINDOWS\system32\defrag.exe
c:
To defrag drive d:
C:\WINDOWS\system32\defrag.exe
d:
To defrag drive e:
C:\WINDOWS\system32\defrag.exe
e:
and so on