Umm.. Maybe assigning each character to an array isn't the best approach.
I suggest that instead use left() for this, if it has any relevence in this situation. I assume it *is* a textbox function you are trying to do, am I correct?
Code:
for (i=0; i<63; i++)
{
PrintString(5+32,5,screen,0,left(BigString,i));
Showpage();
}
EDIT: Be aware that using for() statements isn't the greatest in the case of textboxes.