Thank you for writing.
Since in Q1 2010 we have introduced a brand new theming mechanism, it is no longer possible to use the new themes in an application prior to Q1 2010. Moreover, some of the controls got their renovated versions and the themes for these version can't work with the old implementations of the controls. I will recommend upgrading to our latest version in order to be able to make appearance customizations and also take advantage of all additions and improvements that we introduced.
Should you have any other questions, do not hesitate to contact us.
the Telerik team
Q1’11 SP1 of RadControls for WinForms is available for download
; also available is the Q2'11 Roadmap
for Telerik Windows Forms controls.