If you want to try linux, my advice is to try Virtual Machine. I am using VMWare Player. On Virtual Machine you can install any operating system you want. And changing the OS will not harm your major OS, so you can even broke your new linux and nothing bad happen. Which Linux is the best for start? There is many choices, I picked Ubuntu and I am happy with it. And as it was told, you can try to build Widelands with manual.
If you have any problems with it, just call me - I will be glad to help.
Oh... I have to say that Linux OS is free (no payment needed) and VMWare Player is also free (you install it with time-trial VMWare Workstation, but you can use it after trial).