just out of interest if people want to try the difference here's two nearly identical sites (only difference is the database was copied a few days ago)
www.xtz750.com < Main site on win2k3/winroute firewall/kerio mailserver (P3-800(133)/512Mb)
www.raidxtreme.co.uk/forum/ < Test site on centos5.2/virtualmin (P3-650(100)/384Mb)