I was looking for an easy way to install all the Prerequisites on a new Exchange 2010 install this last week, and ran across a good script that does it all for you.
The script was written by Dejan Foro over at ExchangeMaster.net. You can find it here.
He has several variations of the script: one that lets you choose what server roles you are installing, or one that installs all prerequisites needed if you are loading down a box with all Exchange Roles.
It's also got variations for whether you are running Server 2008 SP2 or Server 2008 R2.
It's available in either ISO or ZIP format.