First off if your going to try and recover your data you will need another 2.5TB of free space to recover your data to. Secondly it will probably take a LONG time depending on whats actually wrong with the drive. A 1TB recovery for me took about 2 days.
There are numerous software options from free to $$$$ that will try and recover your data. Ive had various levels of success recovering my data depending on what was wrong with the drive. So there's no guarantee that the software will be able to recover all your data if any. I'd recommend finding a free one on google to try out first.
For the 320G drive, see if the recovery software can see it. They will sometimes pick up drives that windows wont show in My Computer. If not it might also be a problem with the enclosure, so either put the HDD in a new enclosure or attach it by SATA to your computer if you have a desktop.