I've used a product called "getdataback" before which works very well. There are versions for NTFS and FAT file systems depending on what the drive was previously. It'll allow you to scan the problem drive and recover any possible data onto the 7200rpm one you installed.
Data Recovery Software - Hard Drive Recovery - RAID Data Recovery
There is a trial version so it will tell you what it will be capable of recovering before you decide if it's worth the cash. There are also pirated versions freely kicking around the net but i'll leave that to your own moral judgement on if you'd want to go that route... :)
Just try to avoid writing anything at all to that drive in the meantime, anything you write to it has the possibility of overwriting data you want to recover and makes the whole job more difficult.

