Dear Vasanth,
There is a slight difference between the section 324 and 325. Section 324 says Voluntarily causing hurt by dangerous weapons or means, however section 325 says Punishment for causing grievous hurt. Therefore the difference is of natrue of hurt. In section 325 nature of hurt is grievous. If at any stage the court my any material available on record is of the opinion that the nature of hurt is grievous then the court can convert the case into 325 for punishment of casuing grievous hurt. In this case the nature of weapon also plays a vital role. So the court should be satisfied that the nature of weapon was dengerous.
For difference please read section 321 and 322 of Indian Penal Code.
Read with section 34 means when two or more than two person commit crime in persuance of common intention, then both the person are liable to be convicted for the same offence as committed.