o you mean ./configure --prefix=/usr/local ?
No that's not it, its a option to specify the location of the clamav conf files (clamd.conf and freshclam.conf)
I found help for it easy with the source's I downloaded at home, but I don't have access to that system right now.
I'm running tinycore on a computer at work.
Theres some way to get a look at all the configure options that clamav will accept, but bugger me I can't find it right now, its like my head is on holiday or the source I just downloaded is not the same as the 0.97.3 I have at home