So you've set up your pc to share your files but XBMC doesn't see them.
This is a problem I've encountered on my two HTPC's and two Android devices, I've seen other people with the same problem on the forums so thought I'd post a how to here.
My best guess is its a problem with XBMC and homegroups but I haven't invested the time to fully get to the bottom of it but this is the workaround that has so far had a 100% success rate for me.
You will need to know your pc name and the folders share name.
For this example I am going to use stammie as the pc name and movies as the share name (please note this is the share name shown to other devices not the folder name explorer shows you on the pc)
In XBMC go to videos
Go to files
go to add Videos
choose Windows network (smb)
You will now have a screen with two dots at the top and ok, cancel, new folder and mirror image at the bottom, click/select ok
A pop up box should now have appeared with "smb://" at the top left of it, click/select this smb://
A keyboard popup should now have appeared, at the bottom of this popup is an address bar with "smb://" in it,
click/select this smb:// and enter the full path of the share, so for my above examples it would look like smb://stammie/movies/ , select done on the keypad when you are finished
You can now set the folder as you would local files, I.E. if it contains movies, tv shows or none and the name XBMC will display for it, select ok and you're done, XBMC should now see that elusive smb share
The above will work for music too just replace step 1 with go to music