All you have to do is go here http://www.minecraft.net/download download the exe file. Put it where you want, like your desktop. Double click and open it. If you have Vista, a pop-up will come up and ask if you want to run it, click yes. Sometimes it comes up in the task-bar and you have to click it to bring it up. Then just wait until it loads. Also if you click Start, Control Panel, System you can see what Windows you have. This would be helpful since you know you have Windows but don't think it's Vista.
I kinda ignored it. It seems this one is a spammer when he makes topics :/ I just did my best to help him.