by putting its title, the speaker’s name, the lecture series name, or the venue in the talks.cam Search box; or
by browsing, using the “A-Z” index to look around the talks.cam database. You can browse by lecture series, by date, or by venue.
Using Google and restricting its search to talks@bham. You can do this by adding “site:talks.bham.ac.uk” to the end of your query (without the quotes). This will not work yet as I do not think the site is indexed by google yet.