Go ahead and install it on C:
Then obtain a partitioning program and partition them as follows:
C: Local Disk - Depending on how many programs you install localy on C: I would set it to 50GB just so you have enough overhead. If you do happen to run out of space, you can always repartition to add space from one to another.
G: APPS Drive - Admin Specified
S: Shared Drive - Admin Specified
M: Swap Drive - Admin Specified
U: Users Drive (Home Directory)
This is just an example of what my server looks like at work, I'm in the process of changing it but this is the current config
Whats even easier is using the HP Smart Start if it came with the server, so did it? This will do most of the work for you