The solution above is right regarding last poster's ID, but you shall enable $textLd
of setup_options.php, because information on latest poster comes from 'posts' table, it's not stored in 'topics' table. Enabling this option means your forums front page will execute slower.
Regarding topic starter's link, it could be pretty the same type:
$cols stands for 'main_last_discuss_cell' template and for 'main_topics_cell' template. For topic's author, you don't have to enable $textLd option because such information comes directly from 'topics' table.
Please note that this simple solution would work only if you have forums for registered members only. If Guests may post on forums as well, the link may produce 'user=0' for Guests i.e. link to the not-existing profile. For getting around with Guests, you should modify core files and add new conditions to them, resp. bb_func_ldisc.php and bb_func_vtopic.php.
There are currently no other solutions, because as we think, adding a lot of links to the topic listing pages looks very confusing. Bulletin board's purpose is content, not users profiles. That's why this information is spare. Additionally, some search engines may try to index user profiles instead of a really important content, if you will provide so many links.
So, this is everything we have at the moment.