You can use Google to restrict a search to any website by adding "site:xxxxxx" (where xxxxxs is the domain name) to the end of a search.
Putting + in front of a search term on Google will ensure that that search term MUST occur within the results
So the following search line will look for your pages containing BOTH your username and mine, SOLELY on this site:
+mamyalynne +buenchico site:theanswerbank.co.uk
However that isn't guaranteed to find every thread where we both posted. If you only posted the third response on a thread, and I then posted only the 50th response, there would be no single page with both our usernames on it. Even so, it's worth a try.
Chris