problem replacing brake rotors

[Seth Art]

Hi.  I have a 91 SE-R.  While trying to replace the
rear rotors this afternoon I twisted off a bolt.  I
got the caliper off without a problem but their are 2
17mm bolts that hold an arm type thing that keeps the
rotor in place and is also what the caliper screws
into.   I was able to finally get one of the bolts
loose and was able to take it off (the lower one) but
the upper one after using a lot of force, I just
ripped the head right off.

So my questions.  Less importantly what did i do
wrong?  should i have used wd40?  This is happening
more and more but until now it was just with splash
guards and stuff.   How do i get these old rusted
bolts off without breaking them.

And more importantly... What do i do now?  Bring the
car into a shop?  do you think its safe to drive? I
assembled everything back together and i am guessing
its safe to drive at least to a shop because the bolt
is still in there. i just ripped off the head.  Is
there any way i can get the rest of that bolt out
myself?

Any advice would be greatly appreciated.

-Seth Art
91 SE-R