the problem you have encountered is the draw back to using Win XP home edition and disk management for setting up the partition parameters
when you are booted into windows and use disk managment the external hard drives partition set-up geometery is written to the boot drive
when you formatted your boot drive there went the external hard drives partition info
the best way I have encountered to get your data back is to use this program
http://www.runtime.org/
it has a free scan feature that allows you to scan your external hard drive, then if you can "see" your files they are recoverable after you pay for a license serial key
if you look in disk managment now; I'll bet your external hard drive will be seen as raw or unallocated ????
if you dont know how to access disk management see "my favorite links" in my signature / then look for Disk managment how to in the "format & Partitioning" section