sky warrior,

By far the best value and impressive performance is delivered by AMD Athlon XP processor and nForce2 motherboard. Here in the US, motherboard and CPU can be purchased for about $100 together (check out www.newegg.com).
I've just sold my P3 system and assembled a new one with Biostar M7NCD Pro board and Athlon XP 1800+ overclocked to 2100+ level. Works faster than P4 2GHz at work!

Regarding the sim: RC Plane Master is a pretty good sim, which costs half as much as other serious sims (I've tried them all).

Hope this helps,
Boris