What the bloody hell is the difference between a colon and a semi colon? Tricky question. Luckily, you can find out in exactly three minutes and fifty six seconds simply by watching this video. (Hint: no, a colon does not just indicate a slightly longer pause)
If you found this video informative then you should visit the punctuation section of Videojug.com for more similarly useful videos. In fact if you did not find that video useful then I think you must already be a grammar geek; therefore you too should probably visit their website anyway so you can bask in the pedantic glory of having everything you know about grammar confirmed.
The hilarious comic strip site The Oatmeal, has a highly amusing (and helpful) strip on how to use a semi-colon. Beware though: this website is extremely addictive and should be approached with caution by anyone with a history of procrastination.