interaction, HOW TO , REGRESSION, XXX

http://core.ecu.edu/psyc/wuenschk/MV/MultReg/Regr-SeqMod.doc

Sequential Moderated Multiple Regression AnalysisÓ

Continuous Moderator Variables in Multiple Regression
http://core.ecu.edu/psyc/wuenschk/MV/multReg/Moderator.doc