Originally Posted by Mwenenzi

MEL by a long way. A few minutes walk fron T2 international to T1 QF domestic or T3/T4 VA JQ.

At SYD the international T1 terminal is ~4km from T2 T3 domestic. Transfer by paid rail, free bus (public roads) or free QF bus airside if have QF domestic flight.
If separate tickets 2:00hrs is very tight. More time usally recomended as most USA flights arrive early morning with many other wide body flights--immigration and customs very busy.

Airport info MELBOURNE (MEL) - amenities, transfers, transport
Airport info SYDNEY (SYD) - amenities, transfers, transport
Look at the wiki in those threads

OP's other thread on this trip
QF forum -- Carry-On Weight Restrictions: Qantas vs. Virgin vs. Jetstar (Domestic)
Oceanic AUNZ forum -- Carry-On Weight Restrictions: Qantas vs. Virgin vs. Jetstar (Domestic)