I copied files to a W7 hard drive using a Vista computer and they don't show up on the W7 machine

This has happened to me twice now.  The first time I used an XP machine to copy files directly to a Vista hard drive and when i put the hard drive back into the Vista machine, the files were not there. In fact, I think the copy process damaged the file system as shortly afterward that Vista machine crashed very hard - i never determined what made it crash, but there WAS a "found" folder on the hard drive that had the files that were "missing" and I had to fix the file system using solutions that I found at experts-exchange, including setting the attributes on every single file to read/write.  

The second time, I used a Vista comptuer to copy files directly to a W7 hard drive and the files did not "show up" on the W7 computer.  In fact, the files did not "show up" on the Vista machine when I connected the hard drive back to it.    

SO, why don't files copied to a hard drive using a different computer "show up" on the hard drive's host PC, and how can I make that process work for me in the future?