help with file transfers

I am working on creating a good backup system for all my photos i've shot over the past 1.5 yrs... I just switched to mac about a month ago... my question is my 500gig external hd was my primary backup from 1.5 yrs back... but now that im on a mac i cant store anything to this HD I got a 1.5TB esata external to use with the mac i'd like to be able to back all photos to this HD even from the old 500 gig drive how would i be able to do this..? Thanks.

my problem is solved... thanks tho...