Entering moderator on SPSS

#1
I have the following:

IV: Aggression scale
IV: Social support
IV: Aggression X Social support.

DV: Psychological distress


I am trying to assert if social support has a moderating effect on the relationship Aggression and Psychological distress. I understand this is done through a hierarchical multiple regression. Is that correct?

If yes, when I enter the IV, should I enter the 3 above, in that order, or only the 3rd one? I am using SPSS v. 17.

I'm getting quite confused...

Many thanks for your help,

Valerie