Q:

What is the command line command to limit SQL 2000 server to 640MB of RAM? 

What is the command line command to limit SQL 2000 server to 640MB of RAM?    This is MSDE2000 and so I don't have access to Enterprise Manager. 

A:

Have a go at this:
EXEC master.dbo.sp_configure 'show advanced options', 1
RECONFIGURE
GO

EXEC master.dbo.sp_configure 'max server memory (MB)', 640
RECONFIGURE
GO

If you have to do this via a command line tool you can put that into a .sql file (LimitMaxMem.sql) and do this:
osql -E -S servername -i LimitMaxMem.sql

BTW- Enterprise Manager should hook up with MSDE just fine.   I used to use it all the time.