Alright, I'll edit the first post in this thread but here's a guide for the newest XBMC's.
First off, make sure
you're sharing something and make sure you know your
IP Address.
Go to any category in XBMC like Pictures, Videos, Music, etc.
Click on "Add Source"
Click "Browse"Scroll down to "Add Network Location"
Click "Server Name" (Browse will scan for any SMB Shares. If you don't have it hooked up, or it doesn't show, simply click on Server Name and enter it manually.)
Click on "IP Address"
Put in the IP (usually 192.168.0.# between 1-255) and press E, then Done.
Back at the "Add Network Location" screen, click OK
Find the IP in the list (looks like smb://192.168.0.2 or whatever the PC's Address is)
Click OK once you've clicked on the IP. If you click on any of the folders listed inside, then press OK, it will simply list whatever folder you're currently in on the main screen. Ideally, you can use this to set shortcuts for any folders you want quick access too, but I just keep it at the root so I can browse for anything I want)
Click OK, and then you'll find yourself all the way back at the "Add X Source" screen where X is Pictures, Music or Video. Feel free to name the share if you like. If there's no name given it will simply be the IP.
Set Content will allow you to set a default media type for each share or folder. You can choose between TV shows, Movies and the like depending on what media you are in. This allows the box to grab info from the web according to what you're currently viewing or listening to. It's a pretty handy feature if you have the time to sort your media by type.
Pressing OK will list your PC Share under that category's main screen every time you enter.