As the saying goes "Beginning is half-done", so is the case with Open Source as well. Open Source offers one variety- a whole lot of them, so much that one tends to get confused. But this variety offers you an opportunity as well to experiment with whole.
My recommendation about starting to use Open source is to start at the application level and not at the operating system level. After all, as end user we are looking at applications and products to fulfill our requirements. If you really want to try out some Linux stuff then try out some Live CDs. A Live CD version will allow you to load the Operating system and environment from the CD itself without any need to install it on the hard disk.
To start learning anything new or different, achieving a minimum comfort level is very essential and this holds true for open source also. Open source has lot of potential and to accrue benefits from it, we need to know all but use what suits us best. An example is if you are looking for some office suite, then Open office and Star office are the best bet. If you just want a word processor, then you may look at Abiword, etc.
Whenever you plan to use any open source product, please ensure that you select/ download the correct vesion, for Windows, Linux, Mac, etc.
Open Office could be dowloaded from www.openoffice.org and Abiword from www.abisource.com