Dual-Core CPU

I'm a little cornfused regarding the dual-core. Can I use a single core processor and later upgrade to a dual-core if needed? I'm thinking about buying an Asus Crosshair mobo which has a single AM2 slot. Is the cost for a dual-core processor worth the benefits. I don't do much multi-tasking but of course I,m a flight simmer (FSX). Does a single core AMD processor go above 3500+?
Bubblehead
Bubblehead