As a web developer, you need to be able to test multiple browsers. As a Linux web developer, it can be hard to do that without having a Windows machine around.
With the latest edition of Wine (Windows emulator for Linux) it's not that hard to do. There are a couple of downsides, like transparent images sometimes don't render properly, and there's a bit of a problem with the background around the control buttons, but it works and it renders pages using IE7, which is the entire point, anyway. The biggest downside is the lack of HTTPS or SSL support.
I'm going to make the assumption you are using Ubuntu Jaunty, so you might need to adapt a few things if you aren't.
First, I'd recommend using the latest edition of Wine, instead of the one packaged with your system. This is especially important if you plan on running any recent games in Wine. You can compile your own copy from the sources, or just use the provided repositories from winehq. The package provided with Ubuntu is very old in Internet days, so I don't recommend using it.