Its quite easy. Just partition your drive 3 times. (Hopefully you know how to do that). And if there was a record on the most amount of installs on a single computer, it would probably be alot. But honestly, thats a pretty stupid record to go after.
I don't know if you're familiar with virtual machines, but in Windows 7 (and xp/vista of course), you can run any linux distro you want in a little window. This is GREAT for trying out each distro you're interested in before committing to installing it.
Like stated before, tri-booting isn't much different than dual booting. It's all managed by the bootloader, which is a screen before any OS's load letting you choose which one to boot into (usually each on their own partition)
I don't understand why you're trying to couple two linux distro's together, instead of just a dual-boot with windows...but I totally suggest Ubuntu! Some might consider it the user-friendly linux, which might sound lame if you want hard-core hacky linux, but any linux distro is as advanced as you want to make it. Another I like is Linux Mint (Debian Edition).