Judging by your specs in the Dell Documentation
, you are probably running windows XP. As Qdeathstar pointed out, XP can't recognize more than 2... maaaaybe 3 GB max. Besides that, I don't think upgrading your RAM alone will get you the performance you're looking for. A pentium 4 doesn't fair too well against the CPUs available now. More important that that, you have onboard video which is not good at all for gaming. Flight simulator is CPU and graphics intensive. You are better off getting a new PC. Mainly because you would pretty much have to replace everything in the PC anyway. Secondly, you only have a 304 watt power supply, which I doubt will be able to support a new motherboard, beefed up CPU, graphics card, and extra RAM.