Windows 7: Portable Hard Drive Problem

Hi,

I bought a WD Elements 500gb portable hard drive to backup my pc and to store stuff on there.
When i plugged it in to my windows 7 pc it was all fine at first and detected the drivers etc. that it needed and i was able to remove it, but when i plugged it back in the pc thought it was a local disk (not a usb mass storage device like my vista pc) and put the recycle bin system file on it and i was unable to remove it. Aso, i can only reformat it to exfat or NTFS.

Is there a way i can stop windows 7 putting on those system files and allow me to remove it without having to boot into vista? If i delete the system files from it when i restart the pc it puts them all back on.

Thanks