>For an older application, my colleague needs to change FILES=, in file CONFIG.SYS. How is the CONFIG.SYS file - or this setting - managed in Windows 2000? When he creates this file, it is automatically deleted!

Hilmar,

By default it's Atoexec.nt and config.nt in WInNt\system32 directory.
You can change it in shortcut Properties -> Program -> Advanced...