I would like to schedule my computer to do an automatic defrag on my hardrives around 4am every day. I have 5 huge drives and if I could keep them defragged each day (or every few days) it would be nice. I'm unsure how to schedule these tasks. Does anyone know how?

Windows XP, SP2.

Create new scheduled task.
Start, click All Programs, point to Accessories, point to System Tools, and then click Scheduled Tasks. Then Add Scheduled Task.
Follow the instructions in the Add Scheduled Task wizard.

You'll probably need first to browse for executable.
the defrag.exe is in C:\Windows\System32.

Then modify the command to:
"C:\Windows\System32\defrag.exe C:"
This will defrag drive c:


And then there are some defragging utilities which have scheduler application with them. E.g. Raxco's Perfect Disk, etc.

<edit>
How to use the Windows Task Scheduler: (w/ screenshots)
http://www.iopus.com/guides/winscheduler.htm
</edit>

How do I tell it to run anyways. I have one drive that is about 8% free and I want it to run anyways instead of stopping.

defrag /?
Usage:
defrag <volume> [-a] [-f] [-v] [-?]
volume drive letter or mount point (d: or d:\vol\mountpoint)
-a Analyze only
-f Force defragmentation even if free space is low
-v Verbose output
-? Display this help text

So, defrag c: -f

thanks