Apple is preparing to launch a tablet personal computer in late March or April, with manufacturer partners poised to roll out as many as 1 million units per month, according to an Oppenheimer research note.

Production is starting and should hit mass-market stride in February, Oppenheimer analyst Yair Reiner said.

"The manufacturing cogs for the tablet are creaking into action," writes Oppenheimer's Yair Reiner in a note to clients issued Wednesday morning.

According to his supply chain sources, Apple (AAPL) appears to be gearing up to build as many as 1 million tablet computers per month. He suggests a March or April 2010 launch.

Reiner added that Apple has settled on a 10.1-inch multi-touch display using the iPhone's LTPS LCD technology, not the considerably more expensive OLED technology suggested in earlier reports.

Apple has been approaching U.S. book publishers with what Reiner describes as "a very attractive proposal" for distributing their content: an App Store-type 30/70 split (30% for Apple) with no exclusivity requirement.

According to Reiner, publishers are disgruntled by Amazon's (AMZN) terms, which force exclusivity, disallow advertising and demand a "wolfish cut" of revenue. The typical Kindle/publisher split, he says, is 50/50, rising to 30/70 if Amazon gets exclusivity.

Apple's tablet would make ebooks more attractive for the education market by simplifying functions such as scribbling marginalia.

"We have not adjusted our model to show the impact of the tablet," Reiner concludes, "but we believe it will be substantial. Conservatively assuming 1M-1.5M units per quarter at an average selling price of $1,000 and a corporate average net income margin of 22%, the tablet could contribute $0.25-$0.38 of incremental EPS per quarter."

Apple declined to comment.