Federation Square is something that people have a love/hate opinion of, but it is a great space to photograph.
From there, wander down to the Yarra's edge, and head towards the MCG.  This then becomes 
Birrarung Marr, with nice city views and riverscapes.
You can then cross the river at the Swan St bridge, and come back to the city along the other side.  But then you just missed the Royal Botanic Gardens, [img=http://www.shrine.org.au/content.asp?Document_ID=1078]the Shrine[/img], the Domain...
In the city, check out 
Melbourne Central, with the shot tower enclosed in a glass cone.
Across the road from there (Swanston St) is the State Library, and some funky buildings of the RMIT campus to your left.
In the other direction is Bourke St Mall, which is the starting point for some really nice covered arcades such as the 
Royal Arcade and the 
Block Arcade.
I'd highly recommend you to jump on the FREE 
City Circle tram, which gives you a great insight into Melbourne with it's running commentary, and you can just hop off if you see something of interest to you.  It will take you from 
Parliament House right down to the 
Docklands area too.  The 
Vic Markets are a short walk away from the tram too.  If you get off the tram at Flinders St station, check out the cafes and laneways of Degraves St.
There's a few days worth of activities for you.  Looking forward to seeing how you photograph our great city!  PM me if you need a guide...