Welcome to the Forums.

I suggest getting a new, non-proprietary case and power supply, to start with. Your model of Dell uses a proprietary power supply that will nuke any standard aftermarket motherboard that you try it on, and you would also be up against the problem of the Dell-specific front wiring connectors.
If you need a little help getting un-Dell'ed, click
here for my photo guide to building your own PC.

It's not easy to find motherboards that will use your old PC133 memory anymore, so if you can tell me what your budget is for this project, I can try to find a motherboard/CPU/memory/case/power-supply combination that fits your price range. Also post the details of any hardware you're hoping to re-use (drives, cards).