0 is automatic which means application controlled. You shouldn't need to change this really to be honest. You should also remember that this is setting Windows memory management when you edit the registry, not just for TF2. This could affect other applications you use, particularly video editing, CAD, video ripping.
If you have 2gig of memory or more and are using XP / 2K I'd suggest disabling your swap file which will mean you wont need to mess with any of this crap at all
. Windows will be using approx 300 - 450 meg of your memory, as long as you have a gig or more left after that you don't need any file paging or swap file, hence mine is off .Right click my computer, go to properties. Go to the advanced page and click the settings button under "performance". Go to the advanced page under performance options and click the change button. Select "No paging File", click set and click apply. Restart your machine, job's a goodun. May also free you up a bit of hard disk space too...