Does Linux have a limit on the amount of ram like Windows does?

I am thinking about installing Linux on a laptop (most likely Fedora, as it is the one I'm the most fimiliar with). My laptop has a Athlon X2 64 bit CPU and 3GB of ram. If I install Linux would I need to make sure I get the one compatible with 64 bit cpu or does that not matter? Also how much ram does Linux support? I know that Vista Premium 32 bit only uses up to 3GB.