I have a laptop with a fairly low battery life, I am running slackware 12.2, and am in the process of making a second install that is completely trimmed down to remove almost everything but the web browser and a couple apps, so that I can run it from ram and shut down the hard disk to maximize battery life as much as possible. If the two slackwares run the same kernel, is there some advanced program out there that will allow me to boot into the ramdisk slackware, and if I should want to switch into a full install, wipe the first slackware off the ram and restart from the second without a full reboot?

What about setting up your own runlevel ?. Just "init ?" between them in need.

This is the best idea.

Just using a smaller install won't give you a faster system. So I don't know what the point is.

If you want to load more or less things, that's what runlevels are for. If you want a slicker desktop, you can use a login manager to set up as many different types of sessions as you wish. If you want to load a portion of your install in ram, you can do it regardless of the runlevel you are running, hence that portion will always be "accelerated", or whatever you intended.

If you really want to implement your idea for whatever reason (I can't think of any valid one when disk space is not a constrain which is the case) then I guess you could change to runlevel 1, mount /sys /proc and /dev -obind wherever, and then chroot. That will not unload whatever is on your memory though. So your only and dubious "benefit" will be that you will have a lot more of ram wasted if you decide to enter "the big distro".