among other things Microsoft bought a portion of Apple to keep it afloat after it was all but run into the ground in Steve's absence.
BZZZZT wrong answer.
MS purchased $150 Million worth of
Non-Voting Apple Stock and the two companies settled some long standing patent disputes. The purchase of the
Non-Voting stock was part of the patent settlement and after the agreed 5 years MS sold all shares at a tidy profit. I stress
Non-Voting as the stock was part of a settlement and MS never had a stake in or any control over the company.
Apple agreed to make IE the default browser o the Mac, but continued to ship the OS with Netscape pre-installed as well. Apple dumped both when they introduced Safari. MS agreed to continue to make Office for the Mac for at least 5 years, which they have continued well beyond.
The other terms of the settlement, including what MS paid Apple for withdrawing over a dozen other patent suits, most of which MS would have likely lost, have been kept a secret by both companies.