4GB is considered the "sweet spot" for 64 bit systems. It will run on 2GB, but there's things that you can't do with that amount of RAM, such as heavy gaming, running a virtual machine (VM), which is a computer within a computer, video clips load faster, I could go on and on, but it's not necessary, 4GB minimum for 64 bit is best. If you have expansion slots to make it 6GB, that would be better, but for most home users, it's not necessary.
Not only your RAM, but processor should be considered, too. A quad outperforms a dual by far, and leaves a single in the dust.
BTW, mark3nt, welcome to the forum! I think you'll like it here, this is a great forum, with outstanding support.