Java,
The amount of RAM you need all depends on which OS you are running. If you are running WinXP for example then 512Mb is appropriate, if you are running Win98 then something around 128Mb is fine.
Running K6 II 450mhz is the lowest end for running and is not going to run Flight Sim very well at all, even with all the minimum settings within the Sim.
Take Care,
Richard