I have installed new hard drives ram graphics cards before but that is pretty much the limit.
With this comment I would really recommend you build and install your own computer. It's definitely an enjoyable experience and there's not too much more to it than what you've already done. With this experience you have mentioned, you easily have the skills needed to follow instructions correctly.
However, with your 12% discount at Dell, that may tip it in your favour, so you need to think carefully over this decision.
While I believe Dell build reasonably good computers, you often have a limited upgrade path without doing some major changes. For this reason also, I suggest building your own.
Configuring the BIOS can be pretty straight forward - I know my motherboard manual had quite a few pages in detail about what each setting does. I didn't touch most of the settings, just configured what I knew I'd need. I simply changed the Boot Priority Order around so that it looks for a CD first, then the main hard drive.
Installing the OS is simply booting the computer from the disc (by having it in the drive), selecting your options and watching while it does it all for you
For $1000 you could have quite a nice little system. Let us know your thoughts, and we'll continue further