I know about the kits on eBay that come with solutions and whatnot...but what would I need to get if I wanted to get everything myself...

Would I need sandpaper, an attachment for a drill, polishing solution...please provide a good list of things I'd need...

Any help is appreciated...

This has been discussed over and over again but here it goes again. Basically you will need sandpapers to take off the yellowed layer of the lens, you will need 320, 600,1000 and up to 1200 or 1500 for the final finish. And then with a polishing compound or solution used with a foam padded disc on a hand drill for ease and faster result. You wet sand the lens along the vertical grain of the lens taking off as much as possible of the old yellowed layer, and then work your way up to 1500(remember wet sanded). Once you are done, you can begin using the polishing solution which can be the 3M rubbing compound or you can even experiment with polishing solutions that is used for finishing car paints. Work on it with the hand drill-foam padded disc combo until you're satisfied with the result.

What can you do to keep them from yellowing in the first place?

As my experience tells me, there is no way you can prevent that because the lens are made of plastic and being there exposed to the sun and basically everything, it will just go through the normal process of wear and tear. The only recourse is for you to learn how to deal with it when the time comes. So, when sanding, make sure you pay attention to what you are doing. What I mean is, even though the lens is thick, you don't want to take too much from the sanding job, so you would be left with a lot more lens to sand in the future. The first time i thought about clearing up my lens, i thought about just using plain rubbing compound and polishing solutions. But then, since a good millimeter(approximately) of the lens' surface has been exposed to the harsh environment, you might clear it up with just the polish and the rubbing compound, but there will be those small cracking pattern in a short period of time. And you will end up working on it again because you won't be happy with it for sure. So, the idea is to sand away this layer of the lens that is not in good condition anymore(about a millemeter or more), so that you will have practically a fresh layer of the lens exposed to the environment. And if you will count, my car is 1997, it's about December of 2004 that i did the sanding job. Let's say, the previous owner just ignored the yellowing of the lens, approximately, i have about 5 years before the fresh layer of the lens that i exposed through sanding turns yellow again. And judging from the thickness of that lens, because i have dis-assembled both of my headlights in the past and I've seen it, i have enough until the car stops running or probably by the time the lens has no more layer to shed, i would have saved enough to buy my a new pair. Hmmm.....maybe i should start a piggy bank saving now for a pair of headlights, $10.00 bucks a week is not bad i guess. By the way, i encountered a product online that is supposed to protect the lens and keep it from yellowing. It's a film like coating that you will stick on the lens and the manufacturer says, it won't turn yellow for the rest of the car's life. I don't know how true this is. I remember someone here posting a link to that. Maybe Jeff has the link, as we all know he is the "Link Master" and the "File Keeper"

By the way, does any one know if there are clear lens available for the 97 Catera headlights? Because the one I have are not entirely clear, they have this vertical lines/pattern that resembles those old style headlights. I am thinking that if probably they are clear, then the illumination will be even better considering that i have the HID conversion kit already.