At the time of this writing, for i386 DSL you need at least 16 megs of ram to boot. This does not provide X windows functionality, only console (at boot run 'dsl 2' for console only). 24 megs is the recommended MINIMUM for X windows. Of course, the more ram the better, since thats where you're working, in ram.
You will find that with only the minimum of ram the most you will be able to do is use primarily the preinstalled software that comes with DSL.