Most popular software is available for both the Windows and Macintosh operating systems. If in doubt about a particular software package, ask. Word processing, home finances, and simple game playing can be done with modest hardware requirements. If you plan on playing games that make heavy use of high resolution graphics, you'll want a graphics accelerator card rather than a standard video card. More and bigger usually translate to higher cost.
Many people spend half again as much on software as they did on the inital purchase of their system.
The total cost of a system depends on processor speed, amount of RAM, size of the hard disk, video capabilities, and peripherals. You can make tradeoffs between these pieces to meet your budget. In my experience, you should buy a computer with the fastest processor and the best monitor that you can afford. Most systems come with adequate memory and hard drives for today's needs. Peripherals are the extras that complete your system.