If Windows Communication Foundation .svc files show up in your browser as the textual content of the file rather than launching your service on XP SP2, (e.g. you get <@ServiceHost ...etc...>) your IIS Metabase may have been corrupted by previous beta installation of WCF. Download the CleanIISScriptMaps utility from the .netfx3 website and run it to fix the problem.
Get it here: http://wcf.netfx3.com/files/folders/product_team/entry5648.aspx
Thanks to the blog entry of Wenlong Dong for this tip.