I'll second that. If you have an IDE drive laying around and it's not puking up bad sectors left and right, then plug it in and utilize it. I'm currently on a box that has a Maxtor DiamondMax IDE drive in it for storage (beside an SSD), and it's not giving me one bit of grief. I'm also still running an ANCIENT Quantum Fireball 60G drive in a box that's been up for over a decade (almost 2 decades) and it's still chugging along. Is it the most speedy drive ever? Nooooo...but it stores files just fine. Do I need to spend $40 on an SSD on sale? Nope to that as well. It's there, it's free, and it does it's job.
It's going to fail though this decade though, so it's backed up. If it doesn't fail, no harm no foul...but I'm still waiting for it to stop working. Really, I've had no problems with spindle or SSD drives besides one single batch of Seagate's at the 250G mark (5 RMA's) and one Raptor that I can fully place on my liberal overclocking travels and a weak ICH8 Southbridge of years past.
If it appears fine and if it's for storage, I say run it...but back it up. Or, don't fully trust it and expect it to fail at any given moment. I'd put more trust in those older IDE drives than a 7K 2TB S/ATA drive, that's for sure. I've got some 3TB drives and am running scared...how do you really back up those without laying down more cash just to back those up?
Basically, drives don't just die (usually). They give you warnings and if it's aged you watch them just a bit more. In people years, an IDE drive is pushing 55yo and just aiming for retirement. I see the fear but if nothing is out there tossing flags that it's dieing, let it keep working. Older IDE drives are more...substantial? Not flooded TB units with lower warranties from birth? Yeah, I trust them old farts a lot more than current drives. Run it!