Vista & Dynamic Disks / Spanning

I had one disk containing two partitions - Vista on the first partition (C)
and all my data & documents on the second (D).

I then bought another disk and thought it would be nice to merge it with the
space in the second partition of the first disk so I would have a much
larger D drive. To do this I first converted both disks from basic disks to
dynamic disks and then rebooted to check everything was OK.

However, the system refused to boot until I used a 3rd party disk manager to
set both disks back to basic disks - it boots fine now. This has left me
with a couple of questions:

1) Can I not convert the disk that contains the boot partition to dynamic?
Or is there some other way of doing this?

2) After using a 3rd party utility to convert the disks back to basic disks
I have ended up with an extra bit of unpartitioned space at the end of my
first drive (6Mb). Was the originally reserved and hidden for something? Is
it safe to use?

Also any links to using disk spanning & dynamic disks in Vista are much
appreciated!

TIA