<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/abcdefghijk&hl=en&fs=1&start=15"></param><param name="allowFullScreen" value="true"></param><embed src="http://www.youtube.com/v/abcdefghijk&hl=en&fs=1&start=15" type="application/x-shockwave-flash" allowfullscreen="true" width="425" height="344"></embed></object>
For example, the video below includes some excerpts from Google Chrome's launch, but I skipped to the last part, when Sergey Brin answers some interesting questions.
Unfortunately, YouTube doesn't provide an option to link to a part of the video, but you can still use the embedded player:
http://www.youtube.com/v/w8oPEJiCqi4&start=249&autoplay=1,
where the autoplay parameter is necessary to automatically start the video.
Since there's no end parameter, you can try Splicd, a site that uses YouTube's API to isolate a part of a video.
Related:
YouTube embedded player parameters