The epic first sales week of Halo 3 could bode well for the next juggernaut in the gaming calendar, Grand Theft Auto IV, according to Janco Partners analyst Mike Hickey.

In a note to investors Hickey said, “We expect all of the ... Halo 3 success drivers should also benefit the upcoming GTA IV release.” The slightly less corporo-bullsh*t translation of “success drivers”, in case you were wondering, is an “accelerating and rabid fan base, a current market thirst for compelling high quality content and this iteration’s early cycle release.” That's right, “rabid”!

Hickey estimates that in its first week GTA IV will ship 4.1 million units, reflecting a 20% attach rate to the PS3 and Xbox 360, the game's launch consoles.

In its first week, Halo 3 managed to make £150 million, getting a whopping worldwide attach rate of 46 percent.

Hickey also dismissed concerns that GTA IV missing the pre-Christmas release window will result in poorer sales than the game might have garnered. “Halo 3’s initial retail success was in a non-holiday release period, which could mitigate some investors' concern over GTA IV’s non-seasonal release period,” Hickey said.

Previously, Hickey expected the game to ship 4.5 million in its entire fiscal quarter, but the success of Halo 3 has led him to think otherwise. “After the success of Halo 3, it’s very difficult for us to conceive a more conservative initial ship projection for GTA IV, and believe there is a strong opportunity for considerable upside to our initial GTA IV ship projections for both fiscal Q2 '08 and their fiscal ’08 year.”

With all that said, after a massive first week of in the UK, Halo 3's sales dropped a whopping 79%. Could we be seeing a trend where the hype behind AAA games drives the vast majority of interested gamers to buy a title in its first week, leaving sales to rapidly tail off? Answers in the Forum, please.

You can catch up on Halo 3 in SPOnG's review, and catch our preview of GTA IV here.