Sirflimflam, the java VM also uses memory on top of Minecraft. So it can exceed 1GB but usually it will hover around 1GB max. I don't think it'll ever get to 2GB unless you assign it 2GB. I could actually give Minecraft 3GB because I'm using Java x64 :tongue.gif: I doubt it'd make any real difference though. 512MB is plenty for Minecraft. It will run stable on that (unless you do something insane like plant 15k TNT and detonate it).
To giveit even MORE RAM create a shortcut to the EXE (Alpha only ofc) and give the EXE the parameters -Xmx2048M -Xms2048M and it'll reserve 2GB of RAM. This is the maximum for 32-bit programs (well, the restriction for non-large address aware 32-bit programs I won't argue about technicalities though).