you're didn't given enough information of your PC for any one to give you a good answer.
What you do me mean you have planety of PC power ??? what micro processor. How big ? and how fast ?
How powerful is your vedio card ? what brand ? same as your micro processor.
What vista edition do you have ?

I have Vista..what dose that mean ? it's a memory hog and you're going to run a sim on top of it ?
Look that the g.3 requirement closely..That would be the bare minumum.
Real flight has a demo..you have to use the key board but I'll give you a good idea if it's campatiable
with your PC. yes, yes you'll be amaze..but play with it and keep an I out for screen sticking for a mili sec.
It will bother you over time, if you're vedio is card is not powerful enough.

Reflex also has a Demo..not sure if it works in Vista thou.

there's other sim out there that's around $40
You can unload and test it on your PC to see if it works.

Flight master
Airplane master
Preflight
Clearview

FMS is FREE.. mine looks and runs just fine on my set up. I have flying scernies up the wazoo for my FMS.
maybe it can be a project you and your grand kids to work on also.