On retirement bought a LaCie 1TB Hard disk for personal data from my work PC. IT guy copied everything across for me. I haven't used the disk until recently when set up an old laptop and connected the LaCie to access
data. I was prompted to format disk to the laptop which appears to have deleted everything!! All my family & travel photos and stuff.
You can try using consumer level recovery software, and if you haven't used the drive for anything since formatting it you have an excellent chance of getting most, maybe even all, of the data back. If you've done anything with the drive since then, then more and more data has likely been destroyed beyond what recovery software can deal with and you'd be looking at recovery services.
First of all, don't do anything, or anything more to the LaCie until all the details are known.
What's the model # of the ext LaCie, and how it is connected to a host computer, USB, SATA, Firewire?
Also how long ago was your data transferred to this drive?
What's the make/model of your "old" laptop, running Win-XP or more recent, & do you have access to a recent desktop running Win-7 or Vista
Last, did you "format" the drive when prompted, or just asking now?
That will get the info for someone to give you the best advice going forward.