xl2k and above
XL: How to Modify the Number of Undo Levels
http://support.microsoft.com/?kbid=211922

xl97
XL97: How to Modify the Number of Undo Levels
http://support.microsoft.com/?kbid=162944

(This is an application setting, though. It'll stay in effect until you (or the
user) changes it back.)

Sounds kind of drastic to me.

Rick wrote:

I am running into memory issues in a very large spreadsheet and am trying to
make the settings as 'bare-boned' as possible. I would like to know how to
cancel the UNDO feature. It currently holds 16 actions in memory and I would
like to disable it.

--

Dave Peterson