Yes you can hook your USB drive out of the case to your desktop
But since you say your computer is all IDE, it's likely you will need different cables (both power and data)
that your desktop are unlikely to provide without a cable adapter
(SATA drives use different power cables) and a SATA controller card
(this fits in one of your PCI slots and will require some computer
knowledge to install.
Some computers equipped with IDE drives have SATA jacks and a power supply with a SATA power plug
My older (2004-ish) Desktop has both kinds of drives and my power supply will power either type.
Then again if the HDD inside your USB drive failed because for example... it was dropped?
It's probably as dead as any roman emperor you'd care to name and you have thus lost the data on it.
But you could put any new 9.5mm SATA notebook drive into that enclosure and move on with your life...