How do I install Windows 7 alongside a pre-existing Ubuntu installation?

I purchased a PC six months ago for work related tasks. I do 95% of my work on Ubuntu (web development). Now, I want to install Windows on another partition to play a few games on my relax time. Which steps should I follow? Any suggestions? Every guide I found suggest to install Windows and, after that, Ubuntu. Being this my main development machine, I cannot afford the risk of wiping everything.

First, back up your data. Keep in mind, when installing an OS, over writing data is often a mouse click away.

Second, boot the ubuntu desktop CD, resize your partitions, and make a NTFS partition for Windows.

Then install Windows into the NTFS partitions. You may need to find drivers for your hardware.

Then boot the Ubuntu CD again and re-install grub. You can do this graphically with boot-repair

sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair

See https://help.ubuntu.com/community/Boot-Repair for details.