When its replacement is 7 years old, nobody really should be using the 13yr old XP as a general purpose PC. Since XP, we've had 3.5 new versions of Windows - Vista, W7, W8 and W8.1, and W9 due to be announced when XP support dies, for release next year.
Not connecting it to the internet is no guarantee of safety either. Malicious software existed long before consumer internet.
I still use XP - Rover's Testbook diagnostics kit is flakey enough even on the hardware/software it was designed for, so at best, under Win7, it would have to run in XP Mode, which kinda bypasses the point

. I have no choice to stick with XP, but this is not on a general purpose PC - its on an unconnected laptop thats unlikely to ever see another floppy/CD/USB.
Thats another reminder - W7's XP mode will be equally exposed, so you need to migrate off that if possible.
This shouldn't come as any surprise, as MS have been telling us for years that XP will cease in Spring 2014.