Windows 7 is more or less the same as Vista, which wasn't too much different to XP. If you're going straight from XP to 7 it might take a few weeks to get completely used to it, but it's still essentially the same thing and it should all still work the same way.
Windows 8 is a bit odd, it's really designed for touch screens so the usual things you might need aren't always where you'd expect them to be. I don't find it very intuitive but I don't use it very often - if I had to I'd probably just deal with it.
However, if you're happy with XP for the time being I don't think there's much rush to go out and buy a whole new computer, or even upgrade if you don't want to. Just make sure your antivirus and firewall are kept up to date, and be cautious about what kind of thing you click on and things you install from the internet.
Mitts & Tess - if your husband doesn't use his laptop for gaming or advanced use of MS Office (and doesn't need a CD drive), he might get on alright with a Chromebook? They are very basic, light, intuitive, secure and difficult to mess up by clicking the wrong thing. Also, cheap. The google versions of word/excel/powerpoint don't come with all of the bells and whistles that MS Office does, but they're more than capable of handling most of the things a normal person can throw at them.