You have to purchase the software (map program) and you have to buy the receiver. You will save money by purchasing a bundle (software & receiver). Look at
www.buygpsnow.com and
www.semsons.com for different bundle pricing. Both of these offer aximsite members a discount. Some software such as Iguidance can be installed on a computer and also on a ppc, while other software can be installed on one type of unit. I would suggest you read the various postings in the gps forum to get a better idea of what is out there and how to use it. TomTom is one type of software like Iguidance.