Sounds like Jan's solution is great, I use IRfanveiw here myself and it is also a free photo viewer program that also has a lot of extra functions, one of them being re-size photos. I have used it for years since I discovered it looking for a good free photo viewer for my PC.
When it opens a photo for you up top there are all kinds of functions you can pick and one of them is re size and it also lets you do standard sizes, custom sizes, and even control the amount of compression when you save to JPEG format so you can get a bigger but slightly less sharp pic if you want rather then a tiny and hard to see but sharp pic, plus it will sharpen and all kinds of things too if you poke around the options.
Here's the page for it http://www.irfanview.com/
It also plays almost any video too
I'd check this and Jan's and see which one you like best, they both are pretty small programs so keep the one that works for you.