[SSJKarma]

3 things that comes into play if you have problems with the keys !

1 - you press them to rapidly, like nosoul telled ya, slow down a bit !
2 - you press keys to slow, press em faster a little !
3 - you got an OLD DIN keyboard !
solution to this, none !
reason why this matter...
DIN = keyboard with big round plug.
PS/2 = Keyboard with little round plug.

here is the dif.
DIN = old keyboard that had trouble with things like more then 1 keys at a time, causing the game to have sluggish key response !
PS/2 = today's keyboards that has a better key definition so you can press about 10 keys all together without problem. and the cables inside the keyboards get the info faster then older one !

there is also USB one but them they are the best for that kind of problem !

to put an all-around answer to that.
did you know you can actually push only 2 buttons to do the super ?
example:
shinkuu-hadoken = D,DF,F +HP+MP+LP
become...
SHINKUU HADOKEN = D,DF,F+HP+MP
or any other 2 punches !
so there it cannot be easier then this so deal with it !