There is a recent and excellent diary by 8ackgr0und N015e that describes how one can learn a great deal about Bain - and Romney's involvement in it - through public filings available on the SEC's EDGAR database. Of course, in addition to filings with the SEC, various Bain entities are also required to make certain filings with the states of Delaware (where they are incorporated/organized) and Massachusetts (where they are headquartered). While you have to pay a fee to access Delaware corporate records, the Massachusetts filings are publicly accessible through the Massachusetts Secretary of State's website, here. And, lo and behold, these records provide even more grist for the mill.
You see, one of the numerous Bain entities that filed in Massachussets is called "Bain Capital Investors LLC." Should you decide to pull up the annual reports for that entity, you will find the following language in the annual reports for 1998-2002:
7. The name and business address of the managing members of the LLC are as follows:
W. Mitt Romney, c/o Bain Capital, Inc...
11. The name of each person authorized to execute, acknowledge, deliver and record any recordable instrument purporting to affect an interest in real property... is:
a. W. Mitt Romney...
Now, of course, this doesn't tell us whether Romney actively participated in the business dealings of this entity during his time working on the Olympics (there is one other managing member, who signed the filings), but as one half of the managing members, one would expect that he took more than a passive interest in its activities. The Boston Globe has also picked up on this.