I'm creating an online tutorial for some software and need to include screenshots. In particular, I want to highlight the position and appearance of a given control in a large screen. Given that I haven't got the space to show the screen at full resolution (at least, not alongside the tutorial text), I figured I would use a kind of call-out from a thumbnail. Here's my poor first effort, made in Paint.NET:

Given how long this took me to craft, I'd really like to find a tool to speed things up (and make them look a little more professional!). Preferably a free one, too - or one that has a downloadable trial. The exact style it produces isn't that important, provided it achieves the desired effect.

Can anyone help me out?

Thanks,

Mal.

P.S. I'm using Windows Vista.