In summary, its a way of limiting the google search to sites that you 'trust'. I think the idea is that there are so many sites with bad information that sometimes you don't want results from those sites.
Basically, you sign up as a google user, create a co-op search (it's in beta) and you get a lovely homepage and the code to add to your site so you get a search bar on your site. It's all free (unless you consider signing up to google a cost you can't bear).
You then create a list of URLs that you 'trust' as being good sources of information and you can tailor the search to just search these sites, or to search the whole web and give priority to these sites. You can also pick sites to exclude.
You can allow people to volunteer to add sites to the list that you search, which administrators then control through a control panel. This way your volunteers can create a subset of sites on the internet that they consider good and accurate, leading to better search results. It also means that some of the lesser known sites come up in the results, instead of being banished to page 10 by all the Mercury matches.
I think the mob here could come up with a pretty good set of sites.
The search results are displayed on a Google serch results page but you can also display them in an iframe on your site so you don't lose your visitors.
You can see an example in the top right corner of www.softwaretestingwiki.com. I created this out of interest and started to play. Hopefully some of the visitors to softwaretestingwiki will add to this co-op, but it has nowhere near the community that this site has.
I think the administrator (sir) needs to set up the search, as they need to be able to add the searchbox code to the host website (i.e. sqaforums).
I'm happy to do what I can, but I think it's down to the administrator to initiate.
Everywhere's within walking distance if you have enough time.