It won't suddenly stop working, of course, but there won't be any new patches to plug security holes that inevitably get found and exploited. That's really what 'support' means. And I'm listening to a discussion on the radio about your options if you are still running it.
The obvious thing to do is pay a couple of hundred dollars to MS and get a copy of Windows 8, install that (it will be a clean install, not an upgrade) and learn to use a whole new interface. Except that Windows 8 probably won't run on your old computer because W8 needs more resources (memory, disk space, CPU). Your old 3rd party software will run okay though, probably, if there is enough resource.
What they didn't mention on the radio is another option: Linux.
- It will run on your existing machine, you don't need to upgrade your hardware. I'm running it just fine on a machine I bought in 2005.
- It looks enough like XP to make you feel comfortable enough, probably more like it that Windows 8 does.
- It will probably run your existing 3rd party software. No guarantees, but Word and Excel run just fine under a compatibility product called Wine. Setup is simple.
- It is free. This point would be unimportant if it did not work, but it does work, so I'll say it again FREE (as in beer). You just download it. You don't need your credit card.
- Support is not going away and there is a vibrant community of helpful people. I've never yet had to ask anything, a quick Google always finds someone else with my question, and the answer.
Lubuntu is one of many 'packaging' options for Linux and you can find lots of others, but Lubuntu was specifically designed to look more like XP to the user and to be lighter weight, ie to run on old machines.
You can even give it a quick try out. Download the CD image from here and burn it to a CD, then boot from the CD. The CD gives you the option of running stand-alone (without touching your disk drive, it is all in memory) or installing a system on your disk. Use option one to give it a try.
When you decide you like what you see you can install it alongside your Windows system but you are better off putting in a new disk and installing onto that. The reason I recommend this is so that you absolutely know that you aren't going to press the wrong button somewhere and overwrite you existing system.
You can then put your old drive into a USB enclosure and copy your data across to the new drive.
All this is no more hassle than installing Windows 8, far less if it saved you a hardware upgrade.