I recently setup a test grid control machine. After a couple of false starts, I just let the grid control installer install everything (including the 9.0.1 repository database and HTTP server) with default settings into the same Oracle home, and it works great. The only thing that needs to go into its own home directory is the agent.
Speaking of the agent, be sure to apply the 10.1.0.4 patch to the management
server and any agents you have installed. On Windows I had a problem with
agents not being able to communicate with the server until I applied the