For 2008 R2, you can check the following location and see if the password listed here jarrs your memory:
"C:\Program Files\VMware\Infrastructure\SSOServer\webapps\lookupservice\WEB-INF\classes\config.properties"
Note: Afterall, I think the above is just the sso db pw but if you set everything the same it could be an instant win.
If this was an upgrade to 5.1 and now you can't login, you may consider reviewing the list of valid admins from "vc_admin_users_groups.txt" (if based on your scenario one populated for you). It would be in the temp directory of the person performing the upgrade (i.e. Start > Run > %tmp%).
Folder Location:
C:\Users\<xyzuser>\AppData\Local\Temp
valid admin list:
vc_admin_users_groups.txt
Admins that were removed:
deleted_vc_users.txt
Once you get an ID that you can login into the vSphere C#lient with, go to the permissions tab of the root datacenter for example, and add the appropriate groups that SSO took out (i.e. your server team or whatever). Then login to the web client / sso related stuff.