That's a SATA drive.
SCSI you usually only find in servers these days.
You can get an external SATA case for the harddrive and use it with your old computer.
You can get a newer CPU, AM3 socket will fit your current AM2+ socket but you'll need to do a BIOS upgrade and your motherboard vendor may not support it. Research hard before going that route.
You can look for a replacement for the CPU you currently have but like I said, it's older architecture so you'll need to look for new old stock, refurbed or used. Used will be cheapest.
Replace the mother board / cpu and RAM. You have no expansion cards in your current box and you are happy with it so you don't need a crazy motherboard as it seems you don't use / need the expandability.
There is a Microcenter in Tustin. Go there and talk to them.
Look here,
http://www.microcenter.com/site/products/amd_bundles.aspx
Those are the bundles they have going now.
FWIW I recently built a couple of game testing rigs using the FX 6xxx line of Six Core CPU's and the Gigabyte MOBO. The FX series is AM3+ socket and "should" fit your current motherboard but if they are giving you the MOBO for free then why not just toss another ~$50 bucks at it and stick in 8 GB of RAM and for under $200 you are good to go.
Don't forget what got you into this mess, your card reader stopped working which could be a variety of things from the reader itself to a MOBO issue.
Why spend the money for a new CPU just to possibly end up back in the same place?
FWIW every time I go to Microcenter the sales guys are willing to haggle on price. You might get them to toss in RAM for next to nothing.