Quote: "Well there are some older games which I think would still hold up today if it werent for the graphics"
Totally agree!!!
I think the reason those old games were so good is because they managed to focus on fluid controls, simplicity (a game doesn't need to simulate RL, after all, it's a game), gameplay oriented (as apposed to achievement oriented) and many of tham had amazing soundtracks despite the limitations of the old sound chips.
Getting back on track, if we're talking old games that are already compiled, you'd do best to remake them as even attaining the source code would be little good because the actual coding dynamic would change (unless we're talking really simple games like pacman, nibbles, galaga). Also many PC games were made using very unfamiliar dialects...
This is assuming that the copyright holders allow you to. You see even old software still has a copyright and if it hasn't expired, you could end up in a world of trouble doing a remake, even if it's for non-commercial purposes.
So if you did wanna do a remake, I'd find out who the copyright holders are as they may no longer be the organisation listed on the intro screen (This can happen if the company is liquidated and its copyrights sold, because of mergers, or whatever). After finding out who owns the copyright make a test level or demo video of your remake and submit it to them with a motivational letter that explains your exact intentions. Only when you have permission can you continue. If they really like it, they may offer to publish it for you in which case you may end up gaining a good reputation in the industry.
Alternately, if you have the financial means, you could try purchasing the copyright (you'll need a good lawyer to ensure everything is above board and nobody gets ripped off too).
You could also remake an old game and call it something else and use different graphics and music and change the mechanics a little and prolly get away with it easily although I suggest consulting a copyright lawyer to find out the exact percentage that has to be different to keep you in the clear. Remember a legal consultation can cost you a lot less than a lawsuit from a huge corporation.