Here you can find the instructions for installing RadEditor for MOSS 5.x (the ASP.NET AJAX version): http://www.telerik.com/help/aspnet-ajax/installing-radeditor-in-moss-2007-farm.html
. It's the same for the classic version of the control, but it does not require ASP.NET AJAX. Also you should know that the first time you enable the lists
feature you should be logged as Administrator. There are a couple of templates, which need to be copied in the Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\CONTROLTEMPLATES folder and you need admin rights for this.
For you convenience I attache a working version of the RadEditorMOSS_4_5.chm to this thread. I hope this helps.
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