There is a DataSheet for CodeCollaborator. CodeReview is just a downsized version of the big brother and AFAIK has the same requirements. Go here for the datasheet. At the time of this post, these were the requirements:
System Requirements & Integrations
Browser: IE 6, 7, 8; Firefox 1.x, 2.x, 3.x
Platform: Windows, Mac OS X, Linux, Solaris, BSD
Version Control: CVS, Git, Mercurial, Perforce, Subversion, Vault, AccuRev, ClearCase, CMVC, MKS, StarTeam, Surround, Team Foundation Server, and Visual Source Safe.
Database: MySQL v4.0.18 and higher, MS SQL Server 2000 and higher, Oracle 10 and higher
Eclipse Plug-In: Eclipse v3.1 and higher
Server Requirements: At least 3.5GHz processor, 2GB of RAM, 10,000 RPM hard drives (preferably SCSI) and 100GB of hard drive space on a dedicated server. Database may be installed on the same machine as the web server or requires high speed connection (at least 100mbps LAN).