Thanks much for your replies! I may just bite the bullet and pick up a case from Fry's for my son. They have some inexpensive ones that will house the micro board and allow me to upgrade the psu and video card.
On another note, I have several old units + parts just taking up storage space. Some units date back to 2005. Is it worth it to donate these to charities, or just bring them to the e-waste recycling places?
Yep buying another case is probably your best option.
Donate working towers and recycle the really old and broken.