Do you mean when someone opens the attachment but doesn't save it, where is it on the disk?
if so I believe it is in the %systemroot%\temp folder (generally c:\temp)
"Look! Up in the sky! It's a bird! It's a plane! It's Diaper-Head Boy! (there by my name!) Yes, Diaper-Head Boy, who disguised as my son, Seth, fights a never-ending battle for truth, justice and terrorizing my house!
Resistance is futile, you will be compiled . . . Please!