Samba is the best way to do it. I would avoid the stream servers, personally, except as a last resort if you can't get Samba to work. Samba is really easy. I can send you a copy of my xboxmediacenter.xml file and a brief description about how to set up a Samba share on your computer. The description necessarily has to be brief because setting up a Samba share takes about 15 seconds. It seriously couldn't be easier. Anyway, the file should give you a pretty good idea about how to point Xbox Media Center to the correct folders (Samba share) on your PC hard drive.
If you want this PM me your email address.