"can i run programs off my old HD?"

No, programs need to be reinstalled for them to work on a new drive.

"and if what f.ed up my old computer was a virus, can that also shift into my new computer from my old hard drive?"

Not likely since the drive containing the virus is not running any programs. But I would look for any .exe or .bat files that you do not recognize and leave them alone.


"I read one box and it said the harddrive would have to be reformated before using, but i NEED everything on my old harddrive."

I would give it a shot. If the MBR is in good shape you should see the external from the new PC.


"And what the difference is on enclosures based on price, or what i should be looking for."


Usually features are the difference, USB/Firewire. Some I believe now have SATA interfaces.