I've had to go look for this more then once so here it is:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SchedulingAgent

MaxLogSizeKB - This is max size of the log in kilobytes (duh).  Make sure you edit this using Decimal values.  The default in Windows 2000 is hexadecimal. 

Default - Notice I changed the Base to Decimal in order to edit the value correctly:

Changed to reflect a 1 MB (1024KB) size:

You can also change other values like the location of the log (LogPath) but MaxLogSizeKB is the only one I've needed to change on almost every computer.

The task scheduler log file (located by default here at %SystemRoot%\SchedLgU.Txt) keeps track of the start and finish times of all scheduled tasks.  We use the task scheduler to run almost all of our services and batch processed simply because it is ubiquitous and reliable.  However, the 32k limit is a pain as a busy scheduler will quickly fill this up and the log will begin to overwrite itself.  You'll get one of these things:
[ ***** Most recent entry is above this line ***** ]

to indicate where the latest entry is.  I've found that with our schedule it overwrites itself within an hour or so.  Your mileage may vary but with today's huge harddrives it's often beneficial to trade a small amount of space for a large amount of history.  Keep in mind thought that this does open with notepad.exe to if it gets too large notepad may choke. 

You may also want to check out my article on using the task sceduler as a poor man's Windows Service:

 http://www.pragmaticprose.com/PermaLink,guid,5cc361e3-3940-43d9-8591-fb6f5dd00036.aspx