have never attempted to upgrade / install new operating system......hence question

i have not actually bought win8 yet but tempted for 25 upgrade download before end of the month......

I have an acer 8930 laptop running vista. It has 1 drive with 2 partitions ACER (C and DATA (D. Both approx 140GB with 10GB and 40GB free respectively.

I have read somewhere (I think) that only the partition with the old OS is deleted. Is this correct?

If so, will DATA (D containing all my photos remain? Also if I copy all of my music (inc iTunes stuff) folder to D: will this all be safe?

also general question - will upgrading to win8 be noticeable in terms of performance? Vista seems a bit slow. I use computer for iTunes, photoshop elements, photos etc. nothing too demanding.

also whilst I'm on a roll.......what software will i need to play blu-rays?