Retroanon3

Hey everyone, recently my girlfriend decided she wanted to buy a new desktop PC. She is tired of using her 7 year old family computer which is basically just a piece of garbage. I am going to try helping her pick out a nice PC that is within the $800-$1,000 price range. She plans on buying computer parts to replace the ones that come with her new computer in an attempt to build a really kickass computer. I've never done something like this so I've come here to ask for a few suggestions. She doesn't want to spend any more than $1000 for the computer and the parts. So what would be a good desktop to have her start with and where would I find top-of-the line computer parts such as hard drives, RAM, video cards, etc? I can't build the computer from scratch, so I just wanna help her spend her money in the best way possible to get the most for her money. Thanks for any help.