wget http://dev.gentoo.org/~swift/gentoo/downloads/guide.xsl fails with a 404 error. This makes following Code Listing 2.2: Downloading guide.xsl of http://www.gentoo.org/proj/en/gdp/doc/doc-tipsntricks.xml impossible. The site is OK. http://dev.gentoo.org/~swift and lower levels return blank pages, (so there is something there) or 404 errors.
Looks like you're out of luck Swift's index.html is 0 byte long and there's no download dir anymore.
http://dev.gentoo.org/~swift/gentoo/downloads/guide.xsl has been restored but its not too clever to have a link into a developers personal area on dev.gentoo.org. Long term, the file should be moved to a more permanent home and the document updated.