Accidentally lost data from external HDD
I have a problem I don't know how to solve. Today I bought a netbook and while waiting for the new Ubuntu Unity release to come out, I thought of trying out Crunchbang instead of Windows that came with it. Browsing on my Ubuntu desktop machine, I found a guide for making Crunchbang live USB stick, and i followed the procedure. However, I made a very stupid mistake. The guide said I should enter the command:
sudo dd if=/path/to/iso/crunchbang-10-alpha-01-openbox-i686.iso of=/dev/sdX bs=4M;sync
where "of=...." part should be replaced with the name of the HDD. I forgot that I have an external HDD mounted and mistakenly copied the data to it.
After this, I cannot see the content of my external HDD anymore. Instead, i have this 620mb large Crunchbang-install device.
I know what I did was stupid, but is there a way to get the content of my HDD back? I have some valuable data on it, so any help would be very much appreciated.
PS I haven't formated the external HDD after I bought it, so I believe it used FAT32 file system.