In my humble and personal opinion, if you want an old game that won't get it's original developers any profit ever again anyway, just download it. I'm sure the developers of those games will love it if people keep playing their games.
So just search google for "underdogs", or try to find other sites on your own, cause we can't give links here, don't want Snover getting sued 😉

This is a big topic. Many old games are still protected by copyright laws and it is technically illegal to download them. However, many of the companies that made them are no longer in business, and many of the still existing companies have long forgotten their old titles.

Also, as ChaosFish mentioned it is against the forum rules to post links to abandonware (old games) sites because we don't want to get shut down by angry game companies. It's easy to find them on Google if you look though.

QBasic (It is a DOS programming language) also had great communities years before, and many nice things came out from under them. Although i did not really finish any such game, but i also made attempts to do so, you may check out my site for such ( http://ruch.co.nr ). Sadly QB at about a year before almost completely abandonned, but the works are still around - it is definitely worth to play with some masterpieces of those ages! 😀

Here are some URLs (Note: these are NOT illegal! Hope nobody will think so :p )
http://www.vplanetmag.com/ - It has long reviews on the games too
http://qb4all.com/ - Here a lot of various QB based codings may be found, even i posted a few in the past there
On the other hand Google for QBasic 😀