The computer I am currently using to write the book and develop associated scripts has the following specs:
Now, this is a fairly high-end desktop, but nothing extraordinary. Notice the 64 GB installed RAM. More RAM is typically the cheapest way you can upgrade an existing computer. A lot of the emerging predictive modeling / data science tools manipulate data objects in RAM. Therefore, I recommend getting as much RAM as possible. Also, get a 64-bit operating system so you can utilize more than 4 GB of RAM!
There are other hardware things to discuss once we get deeper into machine-learning. But for now, a 64-bit machine with hopefully more than 4 GB of RAM should do the trick! You ought to be able to run all of the book scripts with 32-bit and less than 4 GB RAM, but it will be slowwww….