Installing Exchange 2007 and its prerequisites is a piece of cake on Windows Server 2003... install iis, add com+ and .net framework, and you are good to go. Not so much with Windows Server 2008... there are more requirements than I could count or care to remember anyway. Luckily those lovely people over at msexchangeteam.com have thrown together a zip of xml files which can be used to do all the work for you.
Here is where the strength of the new windows powershell comes in. The zip of files can be found at http://msexchangeteam.com/files/12/attachments/entry448276.aspx. Unzip all the xml files to the C: drive root, then open up the command prompt and run "ServerManagerCmd -ip xmlfilename.xml" for each xml file that matches a rule set you need. You will likely have to reboot after each one, but the powershell will tell you when its needed.
Credit goes to: http://www.petri.co.il/installing-exchange-2007-prerequisites-on-windows-server-2008.htm