How can I tell OSX NOT to mount some of the drives in my computer?
Create a file /etc/fstab with the following contents.

# fstab
#
# Identifier  mount point  fs type  options1
#
UUID=3CA41C88-3E86-3A39-88CE-9379FF44B6A5 none hfs rw,noauto


The alphabet soup after the = sign can be found with diskutility.

(Fire up DiskUtility, select the disk, right click, More Information Universal ID)

FS tab needs the following ownership and permissions:

bash-3.2# ls -l /etc/fstab
-rw-r--r--  1 root  wheel  71 29 Aug  2011 /etc/fstab


To create the file try this:

sudo nano /etc/fstab


The noauto option causes it to not mount at boot.
In a terminal window type man fstab for other options

Not directly applicable to your problem:  VirtualBox, VMware, and Parallels can run windows in a virtual machine.  VirtualBox allows using a dedicated disk. (Others may, don't know)  For applications that are not CPU or graphics intensive, or access the hardware directly this is often good enough.  I run MS Access this way.  Anything that needs DirectX may have issues or have an unacceptably slow frame rate.  Action games don't work well.