People please when you donate a computer to a thrift store securely erase the hard drives.
One of the systems I have that is dual boot (Windows XP Professional and Slackware Linux) literally came from the trash heap behind a thrift store. Well actually it is a combination of such systems.
Starting out I did need to purchase a cheap case that had the amount of external bays I wanted. I chose a SuperCase TX388.
Then from the three motherboards I had salvaged I chose the Intel D102GGC2 with an Intel Celeron D 3.20GHz CPU and 1536MB RAM. That according to the "slash" screen came from an EMachine. The "spash" screen changed when I upgraded the BIOS to the most current available for that board (GC11020M.86A.1087.2007.0130.1451).
I installed an 80GB Western Digital hard drive and three 40GB Seagate hard drives, all of which were "rescued" from other systems.
In order for all four hard drives to be recognized I installed a StarTech 1 port PCI Express IDE controller adapter card.
I then installed a 3 1/2 floppy drive and two DVD ROM drives.
To complete the "build" I installed a NetGear model WG311 wireless card and a four port USB card.
By no means is it a "top of the line" system but it works.