To redirect a file or site without losing POST data you have to do some configuration in the IIS6.0 metabase to get it working. It took me some time to figure out, but when you know it it’s quite simple.
1. Install the metabase explorer from te IIS6.0 resource kit. Get it here
2. Fire up IIS Manager and rightclick on the site or virtual directory you want to redirect using a 307 Temporary redirect. Choose properties and open the tab Home Directory.
3. Choose “A redirection to a URL” and fill in the new URL. In my example i wanted to redirect traffic from http://example.test.com/ to http://new.test.com/ which is located on a new server. Click OK to Apply
4. Open up the metabase explorer and navigate to [servername] -> LM -> W3SVC -> [SiteID] -> root. There should be a entry whith the name “HttpRedirect” (ID 6011). The data of this entry should be the url you entered in step 3, in my example http://new.test.com. Doubleclick the entry and add “,TEMPORARY” at the end, http://new.test.com,TEMPORARY in my case, and click OK.
5. Now, if you do a post to http://example.text.com/process.aspx it should redirect to http://new.text.com/process.aspx without losing the POST Data. Remember, if you change Home Directory settings via IIS manager, it removes ,TEMPORARY and you have to re-add it.