I suggest the Tiger Direct Msi p6ngm2 Intel barebones kit with motherboard, retail boxed Intel e5200 cpu, and ddr2 memory for $179.99 plus shipping. It comes with a basic case and 450w power supply. Your old dell optiplex case has too many proprietary form factors and power supply connectors. You might be able to sell it separately on ebay for a few $$$. When you assemble the kit, I recommend you place the bare board on a phonebook (non conductive surface) and do a bare bones test before mounting the board in the case. Install the cpu/heatsink, memory, keyboard, mouse,and video connection. Do not connect any optical or hardrives. Connect the 24 pin and 4 pin leads from the power supply to the board. Touch the pin cluster with the power led, power switch, reset, etc. with a plain flathead screwdriver until the board fires up. Enter the bios, set the boot order to cd (or dvd) and hardrive (same as ide 0), save and exit. Then turn the power off, and finish the installation. You may want to remove the power supply from the case for the test, so the leads can reach the board. This will also make mounting the board easier, keeping wires out of the way. Finally, you only need about 4-6 standoffs to match up with the motherboard holes. Standoffs are 1/4 inch brass or silver colored and screw into the side of the case, to lift the board slightly and line it up with the backplate (i/o shield). Install the motherboard backplate and standoffs at the same time. Remove any temporary plate from the case by twisting it off, assuming your kit comes with the motherboard backplate. Any standoffs that don't line up with a hole in the board need to be removed if necessary. Some cases have the standoffs already mounted, some you have to screw them in yourself. Finally, when you are finished installing all drives, etc in the case, when you fire up the system, if you get a windows bluescreen, it means you have to format the hardrive and reinstall windows and install the motherboard drivers on the cd that comes with the board. If you don't have a windows cd, you can buy a dell oem xp or vista cd for about $16 online, and use your old microsoft coa sticker number on the dell case to reactivate windows. Do not remove the sticker; if you damage it, you won't be able to read the numbers. Write them down carefully and test the number before trying to remove the sticker.