Thank you both for your suggestions. I have added the RadStyleSheetManager control that Shonda had suggested and this has resolved some of the problems but not all.
What is still happening is that the top border of the RadEditor is not being shown and the drop down list that appears on the page above the RadEditor has its list items displayed to the screen as well as in the list control.
The RadEditor control is the Requirements field on the page.
The drop down list where its list items are being displayed outside its control is the Contract Type field.
Unfortunately I can not provide you with a url to investigate as it is on our UAT server which is only available to internal staff. What I can do is to attach screen shots of what is happening.
The source code that we are using, along with the css styling that is relevant to this can be found here Source Code
I also attach a screen shot of what the page should like like (taken from IE8).
I also attach a screen shot of the page in IE6 with the issues highlighted in red (Display IE 6.jpg)
I also attach a screen shot of the page in IE6 which shows the list items from the Contract Type drop down list. (Display IE 6 Text Source.jpg). As you can see the items from this list are appearing as text under its control and before the Rad Editor.
I look forward to hearing from you.