There are ups and downs with any operating system.
Windows XP is better than Windows Vista in my opinion, and (most) Linux systems are better than Windows XP (in my opinion).
Most Linux systems are 100% free.
0 Windows systems are free (at least without nasty catches and long contracts).
When people say there is more software for Windows, what they mean is that there is less commercially-available software for Linux. I personally don't think it will be long until we start seeing companies selling software for Linux in shops, because Ubuntu (a big version of Linux) is driving Linux forward, and more and more people are switching to it.
As for the currently available software, there is usually an alternative to any Windows program, and it's usually free. At worst, you will have to run the Windows version of the software using a set of tools called 'Wine' - which lets many Windows applications run under Linux.
Many people also say that Linux can't play games. False. There are many free games for Linux, and many commercial ones too. Unreal (/Epic Games?)is one of the big companies which releases Linux installers for their games (Unreal Tournament since 2003 has Linux installers).
OpenGL (like DirectX, but free and for Linux) is more than able to handle games.
The only reason some mainstream games companies haven't started supporting Linux yet is because they don't see enough people using it, so they don't think it will make them enough money, development costs =]
It's a good idea to dual-boot, if you choose Ubuntu, it should be fairly simple and you can even run it straight from the CD.
As for other distributions, you could try PCLinuxOS, I've never used it but it's got a good crowd so it must be good.
I recently tried a distribution of Linux called Zen Walk, it's *very* quick to start and it's nice to use.
It doesn't hurt to try something that's free
