Editing multiple folder permissions

Hey all,

About a year ago I created a new account on my Macbook Pro. It's a long story as to why I had to do it, but when I did I managed to run into some permissions issues on my external HD.

Some of the folders that I created on the external hard drive using my previous account are now "Read Only." Because my new account is still an administrative account, I can go in and change them to read & write. I've had to do this with a few folders in order to upload music through iTunes. For example, if I upload a new CD from an artist that I already have a folder for, I have to change the permissions on the folder first.

Changing the permissions on one folder is a quick process, however my entire iTunes library is set up this way. I need to change the permissions all of my iTunes folders and all of the folders they contain. I also have a multitude of folders containing my own compositions and recordings that are the same way. Going through and changing the permissions for each folder individually will take me days, so I'm wondering:

Is there an easy way to mass edit the permissions on a folder and all of the folders it contains?

The drive is formatted as Mac OS Extended (Journaled), and I'd rather not reformat it and lose everything. Also, with a new Macbook Pro on the way in a week or so, I'd really like to update these permissions so that they are "Read & Write" for everyone. Is this a wise decision? Will it make the usage of my external HD's contents easier with my new MB Pro?

Thanks!