OK. Now that you have your new shiny PC it's time for the setup. When you turn on your computer for the first time; their is a couple of thing that needs to be done in order get the best service from your piece of hardware. Depending of your necessities, now its the time to choose the suite of programs that is going to make your life a little easier.
It doesn't matter what OS you are running; the first time you turn on your computer, you'll need to setup some basic parameters. This step is really easy; at least on Windows, Macs, or the user friendly versions of Linux (Ubuntu anyone?). You just need to answer a few questions in order to establish the user, password, network settings, etc. After that, the really important decisions have to be made.
At this time; you'll need to decide for what are you be using this machine. if you are a hardcore gamer or a programmer, first of all, this is not for you. You already know (or should know) what you need and how are you going to set this new PC of yours. Now, if you are planing to use this machine as your primary machine, to do everything, their are certain software programs that are essentials.
First of all; you'll need to download the proper updates for your operating system. If it's Windows/MacOS, nowadays, it's going to do it automatically when it sense a internet connection, usually; but in some occasions, you'll need to do it manually. If you are a Linux user; it's going to depend on the distribution that you have . For Windows, just type "windows update" in the Windows search box.
After that, using the web browser that came with your PC (IE on Windows, Safari on Mac) go and download the latest versions of Firefox or Chrome. They are faster and more secure than the other for the moment. After you finish with that installation, you'll need to secure the rest of your system.
Chrome running on Windows Vista
Firefox 3.6.8; running on Windows Vista
These days, because almost every machine is connected, the moment that you turn on your computer you are at risk. There are a bunch of companies that produce anti-malware software; some of them are free some others are not. Most retail machines come with some brand or another, sometimes offering six months to a year of service for free and after that you'll need to pay some amount of money in order to receive malware database updates or updates in general.
What I recommend is to uninstall that trial software (it's part of the crap that PCs comes with); an install one of the free, highly recommended ones, like AVG or Microsoft Security Essentials for example. It's also good to know that you will also need some kind of firewall (the one that comes with Windows is really good) and some kind of spyware/adware removal tool if the anti-malware tool that you chose don't offer that capability. After that, depending what is your inclination on the work/entertaining balance; you'll need to install some kind of office productivity suite and some kind of media player/getter solution.
Microsoft Security Essentials; running on Windows Vista
For work, you need to install some kind of productivity suite. The best one out there is Microsoft Office
. Plain and simple. If you can afford it; it's the best all-around piece of software for producing the kind of documents that most of us need on a regular basis. From the menial word document to that piece of art that you'll need for your blog; it all can be done with Office.I always recommend that if you think that you will need Office, you should get it bundle with your PC if the offer is good or find a nice offer
online for a least the home or student versions. But if you're stuck with MSWorks or Wordpad in the Windows world, you should get a nice MSOffice replacement like OpenOffice.OpenOffice is a great office suite alternative; it has all the basic applications that you'll need to produce a competitive document and it's free and open source. Of course, there is the web alternative, like Google Docs and MSOffice Web Apps, if you don't want to install anything and you think you'll have a internet connection all the time.
OpenOffice.org; running on Windows Vista
Well, you're done installing your productivity suite. Now it's leisure time. There are several media player solutions out there. But basically you just need a piece or pieces of software to play your media and also to get some media.
Apart from the media that you can get directly from the web, from the likes of Youtube, Hulu or Last.fm; it's really good to have some kind of software to play your videos and music. Also, if you are interested in subscribing to audio and video podcast, it would be necessary to have a program that can subscribe to their RSS feeds for you.
If you already have an iPod
; you're already using iTunes; and, it you are part of the few that understood that the ZuneHD
it's a better portable media player, you already familiar with the Zune software. Either way, you already have one of the best products in that category. 
iTunes 9.2.1.4; running on Windows Vista
Zune Software quickplay screen; running on Windows Vista
Another software, that is essential for media playing, is VLC media player. This little software is so powerful, that it even plays broken videos files without a problem. It's true that Windows and Mac computers come with Windows media player and iTunes+Quicktime, but if you need to play that video with that obscure format, VLC it's the solution.
VLC Media Player; running on Windows 7
This list by no means is the definitive rule on how to set up a new PC, but is more or less a good example on how you can achieve a proper functional system without the burden of out-of-date, expensive and resource hog software. After you have this basics apps running smoothly, install all the proper software that fulfill your particular needs and withhold to install all others that are not necessary.
Also; most of the software here presented is free or open source software, tested on Windows machines. Excepting the Microsoft and Google products, there programs are available for the most popular platforms. Chrome also have a MacOS version.