Ok
Any of the suburbs you mentioned are fine.
Fitzroy: very bohemian, arty, laid back. great social scene, pubs/bars (ah I miss Polly's!)
Carlton: Good food, Lygon st ~ very average now.Surrounding streets have great food.
Parkville: never spent much time in, but close to all these.
Good tram network, quick & easy into the city. Many people share houses in these area's attend Melbourne Uni.
I would choose between Fitzroy & Carlton, with Fitzroy #1.
This site may help:
:: House Share Vic :: Welcome to House Share VIC
Otherwise the Uni should have social/student services.