i wouldnt know..dont have that kinda problem..@_@
my parents are very open minded ppl..
and i get along with everyone..including my bf's mom..

my mom and dad support me in everything..and everyway possible..
wutever i want to do..my mom and dad just say "go for it!"
so when i got a bf..my mom just told me not to "do it"..
and she told me..no matter wut my dad says..
if u like him..just stick with him..dont worry abt ur dad..
but my dad didnt say anything..:)
anywho...yeah i agree with guai..
u should understand why ur parents dont like ur gf..or vise versa..
which ever situation u are in..
and then go from there..
if ur gf's reasons are reasonable..then u should consider talking to ur parents abt it..
if ur parents' reasons are reasonable..then u should consider talking to ur gf abt it..or consider break up if it's to serious..