1st: Look around the web for some good Linux documentation.
www.linuxdoc.org and
www.linuxnewbie.org both have good documentation and linuxnewbie has some very helpful people on their BBS. If you want to get a book, I'd suggest Running Linux 3rd edition from Oreilly. It really is a great overall Linux book.
2nd: I would suggest a Redhat distro either version 6.2 or higher. They have a very easy to use installation program and it has alot of additional programs to get you started.
3rd: As far as drive space is concerned, I would suggest about 2GB for Linux. That should cover all of the Redhat packages if you do a full install. You may want to eventually want more space but why spend more money for a hard drive for an OS you may not like!
4th: Now comes the somewhat tricky part; getting all the OSs to play nicely
🙂 You have many different options and I'm sure you will get many varying opinions on this so here are my 2 cents. I would install WinME on the first 5 or 6 GB or so. WinMe will take over your master boot sector so you want to do that first. Win2k's bootloader to be installed last will allow you to choose between the different OSs. Then install Linux on the next 2 GB. In order for linux to boot, it's boot partition needs to be within the first 8GB of the hard drive. There are other, more complicated ways around this, but for simplicity, just try to make Linux within the first 8GB. You only really need 2 partitions for Linux, a swap partition(equal to the amount of RAM you have) and another partition for everything else. Most Linux gurus would slap me silly now for telling you only 2 partitions but for simplicity sake and to just learn, this is good enough. Make SURE you install LILO to the Linux partition and not the master boot record! (Redhat install will prompt you for that also) This will be important for triple booting later. Then install Win2k in the remaining drive. It will see the other partitions so just install into the remaining space. To get Linux to boot from Win2k's bootloader, goto
http://www.enterprisedt.com/publications/dual_boot.html .
This is where I'm not sure what to do about WinMe. I think Win2k will see WinME and make a selection in the bootloader to allow to boot to it. Hopefully, someone out there will post a good link as to how to do this.
And you're done! Just make sure you create a Linux boot disk during install(redhat will prompt you to). Otherwise, you won't be able to get into Linux until the above Win2k boot link is installed.
Hope this helps! Good luck!!