Here is a link to the SQL Server 2005 System Requirements:
Microsoft SQL Server 2005: System Requirements
Nothing specific that I saw about Hard Drive space required - although I do know that depending on what you install it could take a few gigs. Installing the SQL Books online and sample code will definitely cause the installation to bloat.
During the installation, it provides window of what is required for each drive. That will tell you what you need for each drive.
Are there any specific errors that popup when you are installing?