I am facing a similar situation with this here,the only 2 differences being that I am facing the problem with an external HDD and in win7.
I tried this solution here-using Sysinternals Process Explorer to find and stop handles related to the external HDD.I found 2 explorer handles related to the HDD,nevertheless the drive still,could not be ejected from the PC even after the handles were stopped.. What can I do to find what is keeping the drive from ejecting safely.