Linux is a very stable OS. It is quite virus resistant since it is so 'obscure' making it almost worthless to mal-ware writers to target unlike Windows which is EVERYWHERE making it a LARGE and easy target to hit.
That said, Linux is just the Kernel or core OS (Operating System). All the different 'kinds' of Linux are called Distributions or Distros. A Distro is the Linux Kernel with certain sets of software packages tacked on.
You can do anything with Linux that you can do with Windows. ...even games!
Linux has a rapidly growing list of games being written just for it. You can play a lot of Windows games through emulators like Cedega, VMware and the like. But some faster Windows based games don't do as well on Linux even through emulators, so it's best at this time to dual boot your Windows and Linux on your computer to play those few games on Windows that you have that may not 'play' as well on Linux.
You ask such a simple question whose answer is so multi-faceted that the complete answer can not be given here as space is so very limited.
To find out more about Linux start your research here:
http://en.wikipedia.org/wiki/Linux
Move on to here:
http://www.linux.org/
Then on to here:
http://distrowatch.com
Once you've researched those sites thoroughly you can move on to the linux.com site that was given by another answerer. BUT, that site is geared more towards power users and Linux geeks than to newbies. That is why that answerer gave the response she did.
After going through all of the info on those three - four sites, you will be armed with enough knowledge to continue your research even further. The linux.org sight has a place called "User Groups" where you can find a Linux User Group or LUG near you to help you even more! They can supply you with Bootable CDs of various Distros, help you install your chosen Distro and help you learn about it. My LUG has been invaluable to me!
For those new to Linux the distros that are most recommended are:
PCLinuxOS
http://www.pclinuxos.com/
Linux Mint
http://www.linuxmint.com/
Mandriva
http://www.mandriva.com/
Kubuntu
http://www.kubuntu.org/
For those coming from a Windows environment the KDE GUI (General User Interface = what you see when you boot up on your desktop to point and click on)
Take a look at KDE here:
http://www.kde.org/screenshots/
For those coming from a Mac environment the Gnome GUI is recommended. See Gnome here:
http://library.gnome.org/misc/release-notes/2.26/
There are other GUIs to choose from but those two are the most popular.
I hope this helps. Good Luck with your Migration to the Penguin!
You'll be glad you did.
â–ºEDIT: Someone tried to give you the link to Damn Small Linux but pasted the wrong thing. Here's the CORRECT link:
http://damnsmalllinux.org/