This can be used in a 32bit system as well. however your still limited by windows ability to only access 3.5 gb's of your ram, and as stated, if you allot everything to java, then theres nothing left to run your OS, or your web browser, etc.
i would recommend that anyone wanting to do this, uses the system resource monitor and look for java in the list, see how much ram it is already accessing and is using. in most case's players dont need the extra ram because a standard mc install with minimum settings (most laptop players or people with crappy (no offence) gpu's) wont require the extra ram, and the lack of it available to the system could actually impede there performance.
I Also want to point out though that this does not modify minecraft at all, in any way.
What this does is allot more ram to Java. because minecraft launchs with the java binary, you get the extra ram advantage. You should always know how a system command works, before recommending it to others as damage can occur with careless coding.
"This has been a TimeKeeper exploit special. tune in next week kids for a brand new episode of ,"Diodes.... or burnt Shit?" XD