Ideal Computer Specs

(This seemed to be the best thread for this topic, but obviously if a mod wants to move it elsewhere, that’s okay.)

I currently have a computer with the following specifications:

Windows XP, 32 bit
RAM: 2 GB
Hard Drive: 120 GB
CPU: Pentium 4 CPU, 2.8 GHz

With my work on Blender, it has become prohibitively slow. (For instance, I recently built a model of Batman from the old cartoon, and I just had to suspend it because the lag time in many commands, especially in the Cloth Simulator for the cape, was just agonizingly slow, whereas tutorial videos show other people’s computers just breezing through such actions!)

So, I hope to buy a new computer in about two weeks. My budget will likely be about $350. I’ll be buying it used, locally (I’m in suburban Detroit, U.S.) likely through Craigslist. Though I’d also like to get a 16:9 monitor (my current one is 4:3), I expect I’ll likely just be getting a new tower.

My question is: can some people here give me some suggestions about the specs that I should aim for in order to have Blender work quickly? This is especially true for the CPU, since I really don’t have a good grasp of those specs or how they work. But also advice on RAM goals and anything else would be useful.

My current computer is from 2003, it was a gift from my brother, and so I have minimal experience with this, and I don’t want to make a crucial mistake in my purchase, since I have so little room for error. Thanks in advance.