Yahoo has unveiled a number of changes to its search engine this week, adding a new search assist feature, and taking a step towards the kind of universal search results that have so far been introduced by Google, Ask.com and MSN Live Search.

Yahoo says this is the most significant upgrade to its search engine since it took control of its search engine three years ago from Google, which had provided yahoo’s search technology from 200 to 2004.

The new search assist feature is a big improvement for the search engine’s users. It is similar to Google Suggest, but goes further than that, from competing users’ queries as they type to suggesting concepts that are related to the search query.

For example, when searching for ‘Tony Blair’, Yahoo will suggest related areas which may be of interest to searchers, such as ‘prime minister’, ‘downing street’ and ‘labour party’.

In addition to the assist feature, Yahoo has started to present audio, video and image results pages alongside normal search result links, something which has been a feature of recent revamps by the other big search engines.

Video results are now embedded in the search results pages, so users can watch a video without needing to go to YouTube or Metacafe to watch it, while relevant image results are previewed.

Yahoo believes that the changes will help searchers find what they want more easily. The company cited a survey from Harris Interactive which found that just 15% of search engine users find what they want from their first search, and most take three or four searches to find what they are looking for.

With the introduction of the assist feature, and the move towards universal search, Yahoo hopes it will be able to satisfy more user queries, and attract more web users to its search engine.