You can do this with the ndoutils plugin for Nagios. I have successfully managed it, but if your Nagios is large, the load might be too big. Also, it only sends the log entries as single-text-field entries; you need to split them up properly yourself later. There are also utilities to parse the Nagios config data (can pull this out using Perl nagios module, or via the livestatus plugin interface) and upload it into mysql db tables for use by other utilities.
Search for ndoutils and livestatus for more information.
UNIX Systems, ITSS, University of Auckland, NZ
Woe unto them that rise up early in the morning... -- Isaiah 5:11