ClamAV is a major project - in the absence of more direct assistance, have your tried looking through:
...amongst others there. It seems that there should not be a problem as long as you are consistent in your installs and correctly configure the daemon via clamd.conf. I gather the software is supposed to live in /usr/local and the config files live in /etc - by the standard intallation.
i.e. 0.75 probably shouldn't have gone into /usr/bin ... presumably if you try to make an rpm via checkid for clamav 0.75 in /usr/bin you have the same conflict. However you should not have this trouble with the 0.8 in /usr/local/bin
so if you stick the software in /usr/bin anyway - then move the files you want to rpm to another directory? Remove/rename the executable "man" (which summons the man pages) and put it back when you've made the rpm ... that sort of work around ... presumably you are trying to make a binary rpm - so you need the executables, dependancies, and instructions of where the rpm has to put them.
But I havn't found anything consistent about upgrades - however I have not access to the mailing list, which is almost garanteed to have something.