Rewriting the URL - Search Engine Penalties?

Greetings,

I have an e-commerce application written in ASP.NET. I just started rewriting my dynamic URLs in the Global.asax module. The method I use is outlined below...

Code:

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Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)

Dim incomingHTTP As HttpContext = HttpContext.Current
'code to parse the URL to find how to rewrite...
'...
incomingHTTP.RewritePath("default.aspx?Page=" & strPage)

End Sub

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This method works great and allows me to to remove querystrings from the URL. My question is, will Search Engines penalize you for using this method? It seems to me that it is not too much different than redirecting a user to a different page.