Having worked with both, there are some pretty significant differences between SAS and Cognos, and I suspect you're looking at a largely manual process.
But if I was looking at a significant volume of reports to migrate, I would at least investigate costs and success rates of an automated tool. A quick survey shows there's at least one out there which claims to do what you need:
DataTerrain launches SAS BI Automated Report Conversion Solution | DataTerrain.
I've not worked with that tool (nor had to perform such a migration), so I cannot comment on whether it works, nor how much work it might save you.
Best of luck.
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Michael Walter
Business Analyst
TX HHSC
Austin
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