A couple of years ago my motherboard fried. So I had to get a new motherboard. So here's the upgrade path for the box:
1.) CPU upgrade (already done)
2.) Power supply upgrade (done)
3.) Video card upgrade. I had to upgrade the power supply before I could upgrade the video card. The card I'm looking at is the Nvidia GeForce 260.
4.) Remove smaller hard drives and replace them with larger hard drives.
5.) Buy more RAM (max it out to 8GB of RAM) and then install Windows 7 Professional 64-bit.
The old parts don't get thrown away or given away. They are recycled, meaning they get reused in my lab. I have a couple of dead PCs that are occupying computer cases. The dead PC will be taken apart and revamped with the other stuff that is no longer used.
I don't know how long this will take. It totally depends on money, and money is a HUGE factor at this point in time. I hope to complete the upgrade by the end of the year. For now, I'll just enjoy what I've got.