
Behold 'Twitterbox' (I thought Twitterblock would be a little predictable).

Here's the Smart Blocks UI. Because the documentation is included, I'd thought about not leaving any on the web, but here's a complete run down of UI to clarify things.
Block Title - This is the title that will appear at the top of the Twitterbox. So long as a username is entered in the box below it, it will link to your Twitter page. Otherwise it links to twitter.com
Twitter ID - This is NOT your username. Instead it's the 6-digit number found in your updates RSS feed. To find this out, go to twitter.com and however the RSS link in the bottom left:

Mine is 714033 (and you can follow me here on Twitter).
Username - is the bit you add to the twitter.com/ URL to get to your profile. Mine is nikf
# of Tweets - This is the number of Tweets you want to display. Note that it's intended to be 1 only (the CSS doesn't show bullets in lists) for simplicity. If you're wanting more than one, either play with the CSS that's in the block, or contact me.
Border - The colour you want the border
Border Width - The width of the desired border (no need to append px - it's done in the code by default). Putting 0 obviously gets you a borderless window.