I just built two projectors to demonstrate stereo 3d as a final project for a class. I just finished today and want to try some stereo video (I've been cheese-balling pictures by having each projector hooked up to a different computer and opening the left and right eye images separately), but I'm having trouble locating software and videos. Is there a generally accepted standard player for a dual projector setup? Is there a standard video format that it takes? Aren't there some free videos I can download online to check this out? I've heard the word field-sequential thrown around in reference to a stereo format--what exactly is that?

Peter Wimmers stereoscopic player (3dtv.at) is excellent. It supports about every stereoformats. The free version cuts the play after 5 minutes. Full license costs somewhere about 50$ but is well invested money if you ask me.
I don't know if there are any real standards for 3d-videos yet. Myself i save my own in side-by-side, right image first format. These can be viewed crosseyed in a standard player as well.

With dual projectors, most available software are designed so that you connect both projectors to the same computer. Most desktop graphics cards offer two outputs, use DVI to VGA adaptors if necessary.

Peter Wimmer's stereoscopic player is not the best video player in the world but it's the most versatile 3D video player available. It's a must have for any stereo3D enthusiast. Most 3D display manufacturers bundle a licensed version of this software with their screens.

The only industry standard for 3D video is the BluRay3D standard which is brand new and has no software support at the moment, all the BluRay software companies are hard at work at getting this format up and running.
So at the moment we use anything that works with your video player.
Stereoscopic player can support a wide variety of 3D video formats : the most popular is to stack the left and right eye videos side by side or over/under within the same frame. Since you're on a computer you can use any dimension you want, if you have FullHD (1920x1080) pictures, you can go full resolution and stack you pictures in a giant 3840x1080 frame, as long as your computer is powerful enough to read the file. If you want to go easy on the computer you are using you can squash the pictures so that both views fit within a single normal sized video frame, but you loose half the resolution.

Stereoscopic player also supports reading videos which have their left and right eye views in separate files, so if your own content is generated that way, you don't need to combine them, stereoscopic player can read them straight away.

The field sequential video storage format is an outdated technology that was used with DVD players. They worked with shutter glasses when connecting the DVD player directly to an old 60Hz SD TV. It gave headaches quickly because the refresh rate (60Hz) was low but it worked. Now with the digital HDTVs this technique no longer works so you should avoid using it : it often causes bugs and it is less efficient to compress than side by side. You'll still find a few old 3D DVD using this format but it's on the way out.

if you have 6-7 series geforce card, that has stereo driver for dual projector output, you can try the free nvidia stereo player. I also play with that, but i needed more feature, so i buyed the fantastic player from Peter Wimmer.

"I can download online to check this out?"
Sure!
For free 3D sample, if you like, you can download a HD relaxing content from my homepage: 3d-video.hu (dual stream WMV)