I just bought a new system but I have to wait for the memory, another week or so. I have access to 2GBytes slower memory which will allow me to build and test the system. I wonder if I install FSX and register it wheather I have to rgister it again when I change the memory. Anybody have an idea about this, is it more advisable to wait until I receive the memory ?

I thought Microsoft ties in your registration code to the CPU, not the memory itself.I think windows checks your memory size through your bios, not windows itself. So it shouldn't make a difference. I may be wrong on this, or i'm just too old to keep up with the hardware stuff.

You won't need to re-register. I installed & registered FSX, then added an additional 1GB of memory a few days later without any problems. Alternatively, if you are still concerned, install FSX but don't register until after you have installed the new memory. You'll be able to use FSX but without multiplayer support & flights will end after 30 minutes. Since most people seem to spend their first week or so tweaking their system to maximize performance, these two limitations may not be too big a concern for you.

you dont need to, i upgraded and worked fine.