Mac unit sales came in up 2% year over year in July, which according to Munster implies 3% to 7% growth for the quarter that ends in September — roughly in line with the Street’s expectation of 5%.

“With just one month of data,” writes Munster, “it is way too early to make a call on the quarter given ~50% of Mac sales in the quarter typically happen in the month of Sept.”

He adds that international sales are growing faster than domestic for both Macs and iPods, which is why he expects reported sales to be slightly higher than NPD’s numbers would suggest. He also notes that July 2008 was a particularly good month for the Mac, with unit sales up 43% over July ’07, so achieving 2% growth over that is no mean feat. The next two months should be easier in terms of showing year-over-year growth.

Things aren’t looking quite so rosy for the iPod.

iPod unit sales were down 17% year over year in July, according to NPD, which is worse than Muster expected.

But once again, Munster notes that international sales are growing faster than domestic. He also expects a “reacceleration” in September thanks to Apple’s back-to-school promotion, which offers a free iPod with the purchase of any (discounted) Mac. Bottom line: Munster expects Apple to end the quarter with iPod unit sales down 5% to 14% year-to-year, roughly in line with the Street’s expectations (-10%).

One final data point: the average selling price for Macs in July was down 4% from the previous month, according to NPD. That’s a lot better than the rest of the industry, which have seen ASPs fall 19% year over year thanks to the growing popularity of netbooks. Muster’s model calls for ASPs to drop 6% quarter over quarter.