You might need to load the RAID driver for you RAID controller.
I would start there.
Also my Vista drive is currently at 45GB of only program files, not data files. Most room taken up by, Vista Ultimate, MS Office,and Adobe Creative Suite, and a few miscellaneous programs. Consider what you are going to want to run on it before you go with 30GB.
This is what MS recommends
# 1 GHz 32-bit (x86) or 64-bit (x64) processor
# 1 GB of system memory
# 40 GB hard drive with at least 15 GB of available space
# Support for DirectX 9 graphics with:

* WDDM Driver
* 128 MB of graphics memory (minimum)
* Pixel Shader 2.0 in hardware
* 32 bits per pixel

# DVD-ROM drive
# Audio Output
# Internet access