hi,
system requirements for SQL server 2008 • 32-bit systems • Minimum of 256 MB of RAM (1 GB or more is recommended) • 1GB of free hard disk space • must have Microsoft .Net Framework 3.5 SP1 and above • must have Windows Installer 4.5.
to down load please go through following linkhttp://www.microsoft.com/en-us/download/details.aspx?id=25052
hope this will help you.