Set your max heap ( -Xmx) to anumber well below your stated miminum memory requirements.
If someone tries to run your game below the min requirements its their funeral.
My game can be run in 2 ways
i) 300 Mb (excluding some zoom levels meaning alot less maps and arts)
ii 700 Mb (all arts in game being preloaded in memory to be used in the game)
So, for high spec CPU i want to be able to run the second option and for low spec the first option.
Problem is, even with low spec 512 Mb if running the game and it picks option 2 then it will be crawling using virtual memory when RAM runs out.