I'm helping my boss move some websites between a Windows 2003 & a 2008R2 server: we've been running ASP pages as HTML on the old one; not so easily done on the new. Fortunately, some bulk editing fixes this.
*. Nodesoft Search And Replace: text replacement tool; can recurse through subdirectories
*. Bulk File Renaming Tool: this thing is like a swiss army knife for filenames & directories.
*. Notepad2 or Notepad++ : use these for hand-editing files. I've used PSPad on other projects.
Also, don't forget to update any sitemaps. Google has a sitemap generator. (EDIT: doesn't like 32-bit sites on 2008R2 hosts; if you have a problem, remove its DLL from applicationHost.config) (EDIT2: found a decent web-based sitemap generator).