Points to a new marketing campaign this autumn, strong hardware partner support, the PC release and episodic content on Xbox 360.
In a Q3 fiscal 2008 earnings call, Take-Two CEO Benjamin Feder revealed the publisher expects sales of Grand Theft Auto IV to exceed any previous GTA title. The game has already sold 10 million units to consumers.
Feder cites a number of factors which will help the acclaimed title reach this target.
"First Rockstar is launching a new marketing and PR campaign which will start in the fall and extend into the holiday season. Also as a must-have game for all fans of interactive entertainment, GTA IV we believe should receive a boost from the ramp up in hardware sales during the upcoming holiday season," said Feder.
He added: "In addition our hardware partners continue to be excited about the title and are planning to support GTA IV in a major way through early next year. The Japanese version of Grand Theft Auto IV is set for release on October 30 and the PC version is due out in November, both of which will open new chapters in the phenomenal performance of the game."
He also noted that the "release of episodic contents for Xbox 360 in fiscal 2009 will further energize sales of the original GTA IV".
In conclusion Feder added: "Based on GTA IV sales to date, and the factors that I just mentioned, we believe the lifetime Grand Theft Auto  sales will ultimately track well ahead of any previous Grand Theft Auto titles."
According to Take-Two the best-selling GTA title is San Andreas with lifetime total sales of nearly 23 million units.
Thanks to seekingalpha.com for the earnings call transcript.