Actually I would not use windows to try to trouble shoot the issue unless you have to. A better idea might be to use a livecd (Ubuntu for example), which is a closer approximation to WiiMC than windows.
If you boot from a livecd, you can run
smbclient -L routerIP -U guest
Then when prompted for a password, leave it blank and press enter.
If it is setup to give guest access then you should see a list of shares, if it is not then you could see nothing or possibly an error. If you plan on using it with a particular user/pass then change guest to the user you want to use and type the password when prompted.