DPM is a great backup solution for Exchange, and in this download you can size it properly to accommodate your Exchange Server environment.
Download it from here: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=c136c66c-bd4a-4fb1-8088-f610cd02dc51&displaylang=en
Cheers,
Anderson Patricio
http://blogs.msexchange.org/patricio
Twitter: @apatricio