So the PC can see SL and vice versa
Lion can see PC but not vice versa correct?
Try these steps
1. Create a new location on Lion > replicate the issue again
2. Go to sharing preferences > File sharing > options > untick SMB here, Restart. Do the same thing but make sure to tick both SMB inside options and File sharing inside sharing preferences
replicate the issue
sure. Its creating a new internet setup or something to that effect
system prefs > network > click on automatic > edit locations > + > name it whatever u wish > done > apply now