Vista - File sharing between XP and Vista computers

OK, I have a desktop PC running XP Media Center Edition and a notebook running Vista Home Premium 32 bit. The XP desktop is connected to a router (D-Link DI 624) via ethernet cable and Vista notebook is connected wirelessly. I also have a netwrok drive. I have installed a program called Network Magic as well in the hopes that it would help. Via network magic I can acess the network drive from both computers and share files and folders. I can print from Vista notebook (printer is a wired hook up to XP desktop PC). So, obviously network is working in general. In Network Magic I can see the shared folders in the XP from the Vista machine and vice versa but when I click on a shared folder on Vista machine nothing happens at all and on XP machine I get a "Shared Folder Not Available" message. SOunds like a simple permissions problem, right? Well, I have tried everything I can think of to share files. Workgroups are the same, sharing is turned on, programs have firewall permissions, etc. Here's a little oddness: None of the drives show up under usual network places (like "View Computers or Devices" or View Workgroup computers" including the network drive. I can only access the network drive through Network Magic - Network Map - right click and then "Browes Shares". The ony items that show up under workgroup computers are the computer itself and, in the case of the Vista, the router. To top all this off, I had itt all working perfectly before and I cannot for the life of me figure out why I can't share files anymore. Honestly, I have tried so many things by now that almost anything could be wrong but the wireless network works fine - it's just a matter of sharing files. Any ideas on what I'm leaving out? This is driving my not-so-technical brain crazy!!