Thank goodness for the Wayback Machine!
https://web.archive.org/web/20140220200506/http://wwwu.uni-klu.ac.at/gossimit/c/book.htm
There's also this site, but only the "free" files don't require the secret password:
http://www.gambitchess.com/index2.htm
That's terrific. Thanks.
But I remember that the 500 Master Games book was one of them, yet it's not there. Oh well, but it has so many others.
Do you know how to extract the files that ask for passwords even though they're listed in the free section?
I can post the password but will it be against rules to post links to other forums ?
Simple google search can help you get the password and the Ossimitz files are available using archive.org
just use the google keywords,
"gambit chess db books password"
Today I stumbled into the gambitchess site.
Sadly, it seems Mr. Ossimitz passed away, so I don’t think it makes any good to hide the cbv and pgn passwords. If any, he was a truly enthusiast about sharing chess knowledge.
http://www.bcsss.org/2013/farewell-to-long-time-board-member-gunther-ossimitz/
Today I stumbled into the gambitchess site.
Sadly, it seems Mr. Ossimitz passed away, so I don’t think it makes any good to hide the cbv and pgn passwords. If any, he was a truly enthusiast about sharing chess knowledge.
http://www.bcsss.org/2013/farewell-to-long-time-board-member-gunther-ossimitz/
I think you're mixing up the two web sites. I don't think the Gambit Chess site has anything to do with the late Mr. Ossimitz.
This is the password which I get on certain websites after using google.
qcIG7@3wmFt
(try googling the password itself.)
Not sure if it works as I haven't been on these sites for ages. If this is against rules then Mods could delete my post. Thanks.
If all you want is the pgn of games in order to play along while you read a chess book, you can find nearly any game free in chessgames.com. In fact, there are some links there which will bring you to pages which contain the pgn of every game found in some of the more well-known chess books--so that you can literally play over every game in the book without having to search new for each game.
Well done for divulging it, now they'll probably just change it! 
There used to be a site by Gunther Ossimitz in which he put up pgn files of all the games from many different famous chessbooks. I think he was careful not to include the annotations, but only the games unless the book was in the public domain. But he passed away and I can't find those files anywhere. Anyone know where they might be available ?
Barring that, are there places to download the games of various famous books in pgn form? I especially wish I could get Tartakower and Dumont's 500 Master Games of Chess.