I'm slightly confused here. Partitioning a hard drive, formatting the newly created partition and installing an operating system on it, whilst not particularly difficult, is not really something that you could have done "by some fluke"...
As to what you do from here, it rather depends what you want to end up with. Do you actually want your hard drive partitioned into three, with Vista, Windows 7 and Windows Me (surely not!) installed on the separate partitions, and the ability to select which one to use when you switch the machine on? That's certainly possible.
However, I would suggest a different approach. I appreciate that you're new to computers, but have you heard of something called 'virtualisation'? This allows (essentially) an operating system to run in something called a virtual machine. This would mean that e.g. you could have just one partition with Windows 7, but other virtual machines running anything you like. And you wouldn't need to constantly reboot to change from one to the other, because they could all be running at the same time, so long as you had enough memory...
This is achieved by means of virtualisation software such as VMWare Player, which is completely free:
http://www.vmware.com/products/player/. Whenever you want to run a different machine, you just fire up VMWare Player, select the machine you want to run, and off you go! No messing around with rebooting.