well if you use the cheat engine you can get over 900,000,000.
but if you don't cheat here is the maximum scores on scgmd2:
hollywise:7147
this way:11412
truth or dare:10737
quest for your life:7603
super Mario world rock:9340
legend of Zelda rockin:11291
my heart up your @$$:4712
switch vs evil dog round 1:15423
i didnt perfect all the pro songs so i cant tell you the high
scores there. sorry.