problem moving files

I'm from Brazil, then i don't know if my english is correct. But i will try.

I'm a photographer and i have a big trouble. I move 25gb of photos to an external driver to work faster in my mac. And i work well. Now, i was deleting some musics from itunes, and some musics where deleted instead of others. Than, i opened the garbage and pressed command+z. When i saw, the 25gb was be transfered to my computer again. I cancealed the process and copied the directory to the external hd. The system showed that message "theres a paste with the same name. would you like to substitute?" and i clicked yes, because i have thinked that the archives that was in the previous paste will be there, and the system will change the archives with the same name. What was an surprise, all my 25gb os photos is gone!!!!! They ar not in the garbage!!!! Where are they? The sustem changed the directory os 2mb to one with 25bg like that?
Please, help me, i'm crazy. Sorry for the english, mut i'm very nervous.
Thanks

Command Z will undo the last action and it seems that the last action was not what you thought it was. Perhaps now is a time to sort out a good back up policy - if your only 2 units are a Mac and an External HD which you are copying to and from then you are living dangerously. Would be difficult to advise you how to sort your photos as it is bit tricky knowing what you did when u said you "copied the directory to external HD"

Thanks Collin. I've tryed to say that i copied the same directory to the external HD, the directory that was backing to my computer. I have an DVD backup, but only when i finish the post production of the photos.