How to upgrade the custom Render from SQL2005 to SQL2008

there is a CSV Render that writen by SSRS 2005, when i upgrade it with SSRS2008, i found there are lots of changes for SSRS 2008.
like SSRS 2008 doesn't support CheckBox and the namespace for TextBox is also difference between SSRS2005 and SSRS2008.

is there any good solution to upgrade it? i am not familiar with the skills of SSRS Render.

or is there any document that can make me clearly with the difference between SSRS2005 and SSRS2008?

thanks in advance.

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RDL report developer