Vista - Vista installation options/dual boot

I’m very confused by all the discussion of dual boot options and installation
here, particularly because they all seem to pertain to the Vista beta.

I’m planning to buy the actual Vista Home Premium upgrade tomorrow (which
the Vista upgrade advisor assures me I can run on my 6 mo. old HP machine).

I’m leery, however, of doing the in-place installation over my copy of
Windows XP, just in case things don’t work out; I’m thinking it would be
safer to do a clean install and use a dual boot system.

My question is: (A) if you choose to run the setup DVD from XP and choose a
clean install as your choice, does the installation setup inspect you hard
drive and create a new partition for you (with, presumably, options about
size, drive letter, etc.) or do you have to have done a partition ahead of
time, using a partition utility like Partition Magic?

And, (B) if you’ve chosen a clean install on a different partition, when you
restart is it somehow automatically noticed now that you have a dual boot
system and give you the start option choice of which system?

For that matter (C) since the Vista install restarts the system several
times from what I understand, does that cause any confusion?

Thanks for any help