I'm doing Commerce and Arts at Monash Clayton, majoring in Marketing and Psych.
Although I don't know much about the psych program at Deakin, I can definitely shed some light into the Monash one. So feel free to PM me if you have more Qs.
Firstly, if you want to be a actual psychologist, you need to do the accredited program which is 10 units + Honours etc... Usually a major is 8 units, but for Psychology you need to do 10. Some of the stuff you learn are Abnormal Psych (Depression, Anxiety disorders, Schizophrenia, Aging etc...). Then there's the more Social and Cognitive aspect, where you learn about classical conditioning and group behavior. There's also some biological aspects, where they teach you important neurotransmitters and brain areas implicated with certain disorders.
Overall, I found studying Psych interesting, though the reading can be heavy at times. Also, if you did Psych during VCE, you will find most of first yr pretty easy. The only step up from that is learning to write proper Lab Reports and more RDA and SPSS stuff.