Hi... Urh... there are actually TWO other more easy and accessible ways:
1. Click on your main drive icon on the Desktop, and use keys 'Command' + 'I' to Get Info and a window pops up, telling you more than you need to know, besides disk space usage.
If you have a Mighty Mouse, you can also Right Click on the icon and get the same window pop-up.
2. On the Desktop, go to Top Menu Bar > View > Show View Options (or Command + J) and a window pops up.
Check (tick) the SECOND box - Show item info. Presto, now check your Desktop, all your hard drives icons, iPods, removables etc have an extra line below telling you how much space is used, and how much is Free.
Cheers