How do I ensure other computers have access to files on an external (removable) hard drive?

I have a Seagate GoFlex 3 TB hard drive with tons of random videos on it and a bunch of files for my website, etc (lots of random stuff, ok?). Today I tried to take it to my friend's house thinking I could just plug it into his computer and be able to access all the files just like I always have been able to do with other computers using my mini 3 GB flash drive. However, his computer only allowed him to access a few folders on the drive. The rest of the folders kept telling him he did not have permission. When attempting to change the owner (take ownership) of folders and/or files, the system told us that he was now the owner and would let him open folders, but would still not let him open the files (it would only show a file list for the folder). When I reconnected the drive to my computer at home, I still had access to all files like none of the folders or files had their ownership changed. What do I need to do to make all the files and folders on the drive accessible no matter what computer we plug it into, or at least on both of our computers?

Honestly I don't remember ever setting any security settings for anything on the drive. I assumed it would act just like a flash drive would concerning file permissions. Is it possible that a program such as Windows Media Player automatically changed the file permissions without my knowledge?

I am running Windows 7 Pro and he is running Windows 7 Ultimate. His computer obviously had access to the setup files because it installed the device drivers and everything just fine.

Solution 1:

See Evan Anderson's answer to a similar question

Setting ownership and permissions to/for 'Administrators' or 'Users' (as built-in security identifiers) should provide an acceptable result.

As to where your existing ownership/permissions came from... Hard to tell.