Dell keeps trying, but Microsoft then 'punishes' them, e.g.:

Dell's secret Linux fling

,----[ Quote ]
| It later emerged that Microsoft's OEM enforcer Joachim Kempin had
| promised Steve Ballmer that he'd be putting the screws on PC
| builders, or "hitting the OEMs harder" in his words.
`----

http://www.theregister.co.uk/2007/01/09/dell_linux_china/

Microsoft 'killed Dell Linux' - States

,----[ Quote ]
| "I'm thinking of hitting the OEMs harder than in the past with anti-Linux.
| ... they should do a delicate dance," Kempin wrote to Ballmer, in what is
| sure to be a memorable addition to the phrases ("knife the baby", "cut off
| the air supply") with which Microsoft enriched the English language in the
| first trial. Unlike those two, this is not contested.
`----

http://www.theregister.co.uk/2002/03/19/microsoft_killed_dell_linux_states/

There's also this new one, revealed through the Iowa case:

"We should whack them, we should make sure they understand our value,
we should do all of the things you and Brian suggest,"

"I can't imagine he would be this blatant against us if he knew you
were there,"

"If he knew and he is really doing this, then we have some serious
thinking to do around this relationship."

http://www.theregister.co.uk/2007/01/27/microsoft_execs_jilted/