It is far more complicated than that. There are a number of good articles about the strategy for Italy and Austria, but here are my two pennies.
Austria will usually do fine if he just survives the first two years. Geopolitically Austria's situation is not as bad as it looks at the first glance. I like to use this unorthodox map as an eye-opener: http://www.diplom.org/~diparch/regularmaps/diplomap.gif
Both Russia and Turkey face significant bottle necks and a talented Austria can fight the two of them for nearly three years before the defence is finally broken. All this time will be available for finding a diplomatic solution. It is not difficult to find allies against a Juggernaut. Germany should know he is the next in line, England is usually interested in forming an alliance. Especially because Russia doesn't have resources to fight on two fronts. A full scale attack in south leaves Scandinavia open for England.
My favorite is of course to turn Turkey and Russia against each other. I nearly always start from Turkey. It is very difficult for Turkey to win if Russia is strong. And Potemkin's baby Sevastopol is so tempting. Oh, who could resist.
Naturally, even Austria can't take a 3-way attack. If also Italy joins the war, the Emperor is pretty much screwed. However, if this happens, Austria has usually neglected the diplomacy badly.
Italy should understand that the winner of war between Austria and Turkey usually continues to west. Both Austria and Turkey will have true difficulties to find their 18 SC's unless they count in those of Italy.
So for Italy the alternatives seem miserable. No matter whether you join up with Austria or Turkey, you will easily get eaten by your own ally after you have finished the first enemy.
I have personally found two very good alternatives for this dilemma. The first and more obvious is to head west instead. Especially in alliance with England it is quite possible to take France down. Germany is not a bad ally either, but with Germany Italy has to be careful not to get double-crossed. In both cases I usually favor a rapid attack in attempt to prevent France from getting two builds.
The second variant is to ally long-term with Russia. Italy and Russia make a really good pair due to the fact that they don't have to stab eachother at any point in order to make it up to 18 SC's. In fact, Italy and Russia are one of the most natural allies in the game. If Italy and Russia have good chemistry right from the beginning, they can pretend allying on different sides with Austria and Turkey and get these two powers against each other. At a suitable moment, Italy and Russia can simultaneously stab their allies, and voil'a, the RussoRomanos got a jump start to the game.
Please feel free to disagree. :)