Windows XP has two months of security updates left. The last updates will be issued April 8, 2014 - after that they are no more.
What this means is that a computer running Windows XP will become increasingly vulnerable to viruses and other computer malware as it gets farther after April 8, 2014 - virus writers use unpatched Windows vulnerabilities to write viruses that will steal banking information, turn a computer into a remotely controlled zombie, or other bad things.
You can determine if your computer is running Windows XP by visiting this website:
It is almost always best to buy a new computer when one needs to switch to a newer version of Microsoft Windows - a new computer has the faster hardware required to run a newer version of Windows.
If you have to or want to keep your older computer, Linux is the way to go. I recommend Ubuntu 12.04 or Linux Mint 13 -32 bit is for older computers with less than 4GB RAM. Get the 64 bit version if your computer has 4 GB or more of RAM or if you plan to upgrade it to 4 GB or more RAM. Cinnamon, KDE, MATE, and Xfce are the windowing and desktop system used in that version - Cinnamon is probably the closest in looks and feel to the Windows XP windowing/desktop system.