I deleted one of the hard drives when I installed a fresh copy of Windows 7.
I want to recover the data from that drive – can I do that?
Well, if anything got written over sectors with data in it, it'll likely be impossible to recover on a modern drive. Always recover to a different drive
There's a handful of recovery software i've used before with varying levels of success. I tend to run recurva first - it does seem to have a good level of generalised recovery, and has a good, easy to understand UI.
Next i'll try photorec, it tends to focus on specific filetypes, and 'carves' files, so it has a better chance of recovering those files. However it messes up filenames and you need to sort through them
Finally, the method i use when i haven't actually done anything other than formatting, testdisk, this should, if all goes well, undelete the old partition. I'd suggest doing the other two first so you have a better chance of having already recovered your old data should this fail.
And next time, don't forget to backup anything important!