SP1 for VMM 2012 has introduced a lot of change in the way virtual networks can be configured, with the introduction of HyperV 2012.
Some handy guides & links below for configuring virtual networking post SP1
https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CDkQFjAB&url=http%3A%2F%2Fdownload.microsoft.com%2Fdownload%2F9%2FD%2F6%2F9D6B4507-BA5A-4DAE-A08D-4DBFD128FDD0%2FSC2012SP1_VMM_CTP2.docx&ei=2S39UImZIIaQiQfvuoGoBQ&usg=AFQjCNF7OKS4dbo-n2iiGt9LSsNfKxIrBw&sig2=pS6QzoCtNLO-8ypmpcyG_A&bvm=bv.41248874,d.aGc