The client Java version only matters in the editing mode and not for the visitors of the web site. This version of Java is not related to the version used by the SiteVision server.

Classid contains information about which Java version should be used on the basis of the versions already installed on the computer. Normally you would like to use the latest installed, hence you specify:
classid=8AD9C840-044E-11D1-B3E9-00805F499D93
Instead of using a specific version e.g. 1.5.0_11
classid=CAFEEFAC-0015-0000-0011-ABCDEFFEDCBA
classid=CAFEEFAC-0015-0000-FFFF-ABCDEFFEDCBA
Codebase is used for specifying from where new Java versions should be fetched. Here is a list of the available downloading sites from Sun. In the codebase you can also specify the oldest possible version to use.
Use the latest installed version of Java (recommended). The oldest possible version to use is 1.5.0_11. If there is an older version than 1.5.0_11 the user receives a question if he/she would like to download and install 1.5.0_11.
classid=8AD9C840-044E-11D1-B3E9-00805F499D93
codebase=http://java.sun.com/update/1.5.0/
jinstall-1_5_0_11-windows-i586.cab#Version=1,5,0,11
Use a specific version 1.5.0_11. If this version is not installed the user will receive a question if he/she would like to download and install the version.
classid=CAFEEFAC-0015-0000-0011-ABCDEFFEDCBA
codebase=http://java.sun.com/update/1.5.0/
jinstall-1_5_0_11-windows-i586.cab#Version=1,5,0,11
Use the latest version in the Java 1.5 family. The oldest possible version to use is 1.5.0_10. If there is an older version than 1.5.0_11 the user receives a question if he/she would like to download and install 1.5.0_11. If there a later versions of java 1.5 available the user will receive a question if he/she would like to download and install the version.
classid=CAFEEFAC-0015-0000-FFFF-ABCDEFFEDCBA
codebase=http://java.sun.com/update/1.5.0/
jinstall-1_5_0_11-windows-i586.cab#Version=1,5,0,10
On Sun´s web site you find more information about classid and codebase for applets.
http://java.sun.com/j2se/1.5.0/docs/guide/plugin/developer_guide/using_tags.html
http://java.sun.com/javase/6/webnotes/family-clsid.html