I am going to install exchange server 2010 on a server 2008 SP2, for more information on Exchange 2010 Prerequisites, see http://technet.microsoft.com/en-us/library/bb691354.aspx
1. Install .net Framwork 3.5 SP1, you can download the full package version from here
2. Install Windows Remote Management (WinRM) 2.0 and Windows PowerShell V2, download it from here
3. On servers that will host the Hub Transport or Mailbox server role, install the Microsoft Filter Pack. Download it from here
4. Run "ServerManagerCmd -ip Exchange-MBX.xml -Restart" from the scripts folder on a exch 2010 installation CD.
5. Prepare schema by running "setup /PrepareSchema"
6. Prepare AD by running "setup /preparead" (setup /PrepareAD will automatically perform the PrepareLegacyExchangePermissions )
7. Prepare domain
Run setup /PrepareDomain or setup /pd to prepare the local domain
Run setup /PrepareAllDomains or setup /pad to prepare all domains in your organization.