Solution found to problem mounting Windows 7 64 bit share

After quite a bit of debugging I found out what the problem is:
Windows 7 apparently requires a proper netbios name to be given to it.
This can be done using the "servern=" option. By default mount.cifs
will use "*SMBSERVER" which it does not like. My understanding is
that the last time this particular thing was a problem was with
Windows 98 and ME (!)

For example, in my case the proper mount command is
mount -t cifs //pirin/c /mnt -o servern=PIRIN,username=yanko,ip=192.168.1.12

By the way, the netbios name must be capitalized. This is the first time I ever 
saw Windows requiring something to be case sensitive.

Hope this helps someone down the line.

Yanko