>it said that the hard drive was not formatted with the Mac I could
>only view not view and 'read'.
Yup. That means your hard drive was using Windows' NTFS filesystem, for which Mac OS X has read-only capabilities. If you wanted to give yourself the ability to write to the drive, you should have used something like this.

>followed some instructions which somehow led me to erase all my data.
The Mac did exactly what you told it to, then. ;-) If you want to change a filesystem type, you're going to have to erase it and start over, and that is precisely what formatting does.

The real question is how did you erase the hard disk? I presume you used Disk Utility to accomplish this task, correct? There are different methods of formatting, if you've used the default method, you're probably going to be able to recover most if not all your files. If you chose to write zeros all over the disk, you're going to have a much harder time.

In any case, don't use the hard drive right now. Unplug it from your computer; you don't want to damage any remaining data. I don't really know much in the way of recovery software, but I dug up these threads here, take a look at them:
http://www.daniweb.com/forums/thread56205.html
http://www.daniweb.com/forums/thread8866.html

Like one of the other posters mentioned, if this is really valuable to you, you should probably take this into a professional data recovery place. A simple tool that you download or buy probably won't be good enough to get everything.

And of course, the lesson to be learned here is always backup! I learned this the hard way, and it seems you have as well.

Yes I used Disk Utility to try and format the hard drive and used the default method. So are you suggesting it's more worthwhile buying software to recover this or take it into a professional data recovery place. I can't think of anywhere near me that could help me with something like this, and these programmes seem to be very expensive. Hmm, is there no easier option?

I would recommend buying recovery software first, since it's quite possible you will be able to recover most of your data. And yes, professional data recovery places charge a small fortune to retrieve it, but they have far more sophisticated tools and methods for doing such a thing.