Hi erickj76,
There are heaps of options in both Melbourne and Sydney and I’m guessing thatr when you say you want aggressive riding you mean more technical stuff so heres a short list of places that are not too far from the CBD’s. I have more knowledge of Syd tho however Melb(Victoria in general) has some amazing trails some a little further from the city.
Melbourne/few hours away
Lysterfield xc
You Yangs All
Forrest xc
Beechworth xc/fr(maybe under renovation)
Mt Beauty xc/DH
For long downhill and lifted riding go to the alpine resorts such as Mt Buller
Many more places, just ask local bike shops.
Now for Sydney.
There is alot of riding within a 2 hour drive of Sydney some of it legal and some not so(Ask a local when youre here). Youre best bet is to get on http://www.trailflix, farkin.net and http://www.nobmob.com and check out some maps. Both sites have social rides. You can PM me on nobmob(paul_j if you like and I’ll point you to the not so legal FR areas and If available show you round.
If time permits and its purely a riding trip, then start at Forrest in Victoria and work your way north through Victoria, the Snowy mountains, Canberra and into Sydney. It all depends on exactly what type of riding youre looking for.