The way the PHP code for Lifestream determins paths is not cross-platform friendly it seems. The icons don't work when hosting WordPress on the Windows platform.
I've tried several variations of custom paths in the "advanced" settings for Livestream "Icon Directory".
The type of path that Lifestream generates is like this:
"http://www.trevormay.ca/wp-content/D:/Hosted%20Sites/trevormay.ca/www/wp-content/plugins/lifestream/extensions/twitter//icon.png"