in itunes select edit and preferences, click the advanced tab and somewhere near the bottom it'll say show itunes icon in system tray, version permitting but it should be similar on any version.
Edit: misread the post, thought you said in the system tray not next to
Right click on the taskbar, then go to toolbars and click iTunes. The next time you open iTunes and minimise it, it will minimise to the taskbar just like you have described.