This comes from experience of having problems installing Windows Vista on my primary desktop after following every little bit of Microsoft advice and guidance. Well (and not trying to sound rude here) but there guidance didn't guide me to anywhere vista related, instead I was guided to the Windows XP installer after I had to downgrade back to XP after the installer failed several times, but with this I can offer my own personal experience to hopefully help people who are looking to buy Windows Vista.

1. Use Microsoft's Windows Vista Upgrade Advisor tool to scan your machine.

Microsoft released a upgrade advisor tool when it released Vista to help the user determine if him/her's machine is ready for Vista. This tool can be located here:

http://www.microsoft.com/windows/windows-vista/get/upgrade-advisor.aspx

This tool is absolutely neccersary as it will tell you about crucial problems (If any) that your PC may encounter when you install Windows Vista.

However don't use this tool thinking that it's 100%, I have proven this by sharing my Vista problems on my Primary desktop PC and how the installer would lock up on me, and the upgrade advisor had no problems with my hardware (And im still yet to find out what piece of hardware is causing it, as I proved some hardware was bad but the upgrade advisor didn't detect it)

2. Investigate into your hardware further

Like I said from personal experience don't take the upgrade advisors word for it, do some research on your machine's hardware and see if anyone has reported problems with it. This will require you to do alot of Google searching (And other searching), but in the end it's got to be worth it to avoid troubleshooting hardware that you could of addressed earlier right?

I'd recommend looking at technical forums that are generally talking computers and stuff like that.

3. Check your USB/Other devices

By devices I mean things like printers, scanners, webcams, headphones etc.. The Windows upgrade advisor should pick up these additional devices and address any issues (If you had whatever devices you have plugged into your computer at the time of the scan) but again why not do some additional work and google around to make sure your devices are going to be supported in Windows Vista, because if you don't check them and find out when you come to install that all important printer and there's no Vista drivers for it. You are seriously screwed!

4. If you current hardware is fine for Vista, check for vista drivers

So if you've made it this far and your hardware is fine to run Vista, I'd recommend you go and check your current hardware setup for Vista drivers. Example you might want to find out if your current Graphics card has Vista drivers written, or maybe your sound card. You can do this by going to the hardware vendor's website and looking up your hardware, you'll soon find out if your going to be able to obtain Vista drivers for your hardware!

5. Choosing the right Vista Edition

Windows Vista comes in 4 editions (Yes there are 6 but im leaving the other two out as there insignificant for this guide) The editions are:

Windows Vista Home Basic:
The bare minimum of Vista, you basically get a upgrade of XP, thats it.

Windows Vista Home Premium:
A step up from Home basic, you get Aero, Windows Media center, Windows Security features and more. Basically the ideal choice for a average home PC/Laptop

Windows Vista Business:
The recommended option for the business user, you get Aero but not Windows Media center. Instead you get all the networking features and advanced backup features that Microsoft thinks you would need if you are running a office business

Windows Vista Ultimate:
It's the big one! That includes all of the features that come in the other three versions. It's also the top of the line version and if you want to spend £249.99 on it go for it, you big spender you! But beware it's also the most demanding on PC resources, so your going to need a decent machine to run it smoothly!

To learn more about Windows Vista version please go here:
http://www.microsoft.com/windows/windows-vista/compare-editions/default.aspx

(As Microsoft are much better at pitching there sales crap than me)

Well thats my guide on things to do before installing Windows Vista. I hope it helps you!