So you have decided you want to get into SharePoint, but you find out that you need to have a pretty strong machine to run it. Actually the latest SharePoint 2010 needs 6 GB of RAM as a starting point to run well and a 64 bit Windows 2008 operating system.
You could actually learn without installing a thing! Yes. Microsoft offers a great service called MSDN Virtual Labs. Using these Virtual Labs you can test and try almost every Microsoft technology and product. And of course SharePoint Virtual Labs is one of them. In the Lab courses you get to learn and have hands-on experience. They even include software which you would need like SharePoint Designer. Really helpful.
So go on and have fun