MS Flight Simulator 98 should run fairly well on your system even though it is getting on a bit.
If you want to improve the performance of the game I suggest upgrading the memory to 128mb (cost you about £30-£40)
..or you could go out and buy a decent graphics accelerator card that uses up to date rendering and refreshing technology. (Will cost you anywhere from £50-£400)
On a final note MS Flight Sim 98 is not a flight Sim until you've bought a joystick - it is simply a must. Go out and part with some serious cash and do it properly.
A force feedback joystick would be a great add-on but a standard flight joystick with a throttle control is just fine.
Rudder pedals I don't know about - never used them or tried them so its unchartered territory for me.
Try
www.cclcomputers.co.uk
they are a decent company who offer goods at extremely competitive prices. They are based in Bradford but will deliver all over the UK. You can even buy online.
Hope this helps