Although there's a lot of software in a Linux distribution, the desktop will run on computers with fewer resources than WIndows XP thru 7.

I have an ancient Compaq Presario V4000 (512MB, some tatty Celeron or other, you know the drill) that my mother was going to scrap. It had Windows XP Home on it which, when freshly installed, was fine; once it had been loaded up with all the bits and pieces that are required on top of a base WXP install to make it useful, it was a dog.

It's now running Linux Mint 9 and is more than adequate for running Firefox, Evolution and other internetty things. I have no doubt that it would make a fine, if slow, development box.