I'm installing the windows 2008 r2 server OS (on a pc, as an experiment, before doing the real thing on our server). I need to have three partitions: C (35gb) - where the OS will be, E and F (each with half of the remaining space). When I get to the relevant point in the installation, I get a screen that shows me two lines :
line 1: Name - disk 0 partition 1, 74.5 GB, free space: 66GB, system.
line 2: Name - disk 0 unallocated space, 9 MB, free space: 9 MB.
When clicking line 1, I get the options to refresh, load drivers, delete, extend, format. If I choose delete or format, I get a warning saying that I might delete system files from the manufacturer. Should I choose any of these options (in order to change the partitioning)?
(When clicking line 2, I can refresh, load driver and New.)

So how do I do it? Which option should I choose?

ok. so I got over my fears, clicked the delete option and the rest was pretty straightforward.

After you deleted the existing partition if should have been converted back into unallocated free space.