Help streaming media from PC to Xbox 360

I've almost got it, but I still need help sorting a couple of things out. What I would like to do is to be able to access all of my music and videos from my computer and external hard drive, on my Xbox, through my router. I am using the Microsoft Security Essentials antivirus and firewall, and no third party antivirus/antispyware or firewall programs.

I have an Xbox 360 Elite, not one of the new wireless versions. I went into HomeGroup on my computer and checked 'share media with devices' and also checked music, pictures, and videos. So far I can play music on the Xbox by going to the music app and choosing my PC. The problem is, I can only play songs that are directly in the Music folder on my computer. And only certain songs at that, I'm not sure why. I have a subfolder within Music called Full Albums and I cannot play ANYthing in that subfolder. What am I missing?

Also, is it possible to access music and videos on my external hard drive? Provided my external hard drive is connected to my computer of course.

Lastly, I can't access anything unless I disable Windows Firewall. How do I set up an exception for the Xbox so that I don't have to disable the firewall every time I want to do this?

Any help is appreciated. Thanks.

Anyone?