I was trying to remember what my first FSX machine was last week, for some reason. I think it ran at a whole 1.8GHz on XP, which was pretty quick at the time (but not really quick enough). I didn't discover add ons until the next machine, running 32b Vista at 2.4GHz. No idea what the graphics card is. Like you, it has remained my 'other' machine since being demoted. It's ~12 years old now.
Still, 'my' first FS machine was a Commodore 64. For those too young to know, that had 64k (yes, sixty four kilobytes) of RAM. I think the 5 1/2in floppies held 640kb. Some started with a Vic 20, which I think had 4k, or a lofty C16. Seconds per frame was the order of the day. But there was some good stuff on a C64 - anything by Microprose/Sid Meier. Software was horrendously expensive where I grew up. P3D Pro, inflation and capability adjusted, is a steal by comparison.