How to stop Windows 7 locking shared media folders

Hello again from a really infrequent poster. I hope you folks can help me out a little with this problem/puzzle however.

I stream media to my Xbox 360 from an External Hard Drive using Windows Media Player 12. This works faultlessly.

However recently I went to stay with a friend for a few days and took the External Hard Drive in order to watch some movies while there.

However when plugged into his media PC (which is still running Windows XP Media Centre) none of the media (movies and music) was accessible.

The folders showed as 0 in size and they could not be opened.

In the end I had to use a recovery software to pull the media from the folders.

Obviously this is not an ideal solution whenever I take my hard drive anywhere, so is there a way to stop Windows 7 from taking ownership and locking down these files and folders when I take the drive to another PC?

So I take it by the lack of responses that there is no way to stop Windows 7 from taking ownership and preventing files from being used on another PC.

Very annoying. I'm going to have to look into things like PS3 Media Server to do the job, which I'll find annoying as I hate installing extra things when a perfectly good (well until this issue) solution is already built in.