How can I avoid "write delay": errors when copying files or backing
them up to an external hard drive connected via USB 2.0 and formatted
in NFTS. This happens when I am copying from a Maxtor ATA drive, as
well as a pair of Western Digital drives in RAID 0. I use WinXP.

Western Digital drives are not realible!
But, try to download the newsest drivers from the internet.

Write delay errors are from a feature of windows xp called Write Caching.  
It can be disabled by:
1. Double-Click on "My Computer"
2. Right-Click on the removable drive
3. Click on "Properties"
4. Click on the "Hardware" tab at the top
5. Highlight your drive
6. Click on Properties
7. Goto the "Polices" tab at the top
8. Click on the Bubble next to Optimize for quick removal.
8b.If that option is grayed out, then uncheck the checkbox for "Enable
Write Caching".
Hit okay, then okay again.  Thats it.

Alternately, whenever you are ready to remove the drive, double click
on the USB icon (A green arrow), highlight the device you are getting
ready to remove, and click remove.  Then it is safe to remove this
device.

-Jcp

jcp's solution does not work. With the setting she/he suggests there
are Write Delay errors.

This document
http://support.microsoft.com/?kbid=330174
at the site of MicroSoft describes several possible causes for your
problem. You can read is and see if your problem is discussed.

Also make sure you apply all availible Windows update. This can be
done via www.windowsupdate.com

By the way, do you have a ATI video card?