Trying to compare computers-please help

I know this isn't the typical place for this but I don't know where else to go.
My parents are trying to get a decent computer and not spend too much on it as they cannot afford the "deluxe" model. They want it fast, able to retrieve music and your typical Windows. They have looked at some Gateways that have Windows Media Center and I am not familiar with this.

What should they get for memory and a processor. I know this is pretty broad but I only know of this information I don't really know how these things compare.

They have also looked at Dell.

Any input would be greatly appreciated!!

Thanks, C*