Macs are likely to be the "key" to a high-performing fourth financial quarter from Apple, says Piper Jaffray. Previewing tomorrow's results call, the firm suggests that Apple will announce shipments of 2.8 million Macs, as evidenced by sales growth of 32 percent year-over-year for the combined months of July and August. Piper notes that this is further based on estimates of 23 percent growth year-over-year for September, which would only be a continuation of Apple's patterns, rather than a surpassing of expectations. Apple is said to have been helped by its Back-to-School promotion, which lured shoppers with free iPod touches and nanos.

Boosting the company further may be the iPhone 3G, which launched early into the quarter and has so far exceeded expectations, having shipped over 1 million units during the first three days of worldwide availability. Actual sales for the fourth quarter are predicted to be about 5 million, as compared to Street estimates of 4.5 million.

Available iPod figures are said to be approaching 11 million, instead of the 10.8 million proposed in Street consensus. This would also represent growth of 8 percent year-over-year instead of 6 percent, a figure which may again have been helped by the Back-to-School deal.