You're trying on n900, I guess, you should probably mention that.
The conkyforecast package wasn't created by me, and the guy that built it didn't say he tested it either. It might not work at all, or may need some special steps to get it working.
Did you read this?
http://ubuntuforums.org/showthread.php?t=869328
If you try to sign up for the weather.com api key it's not free anymore...

These guys did it over using a different weather service and using lua, maybe a better starting point:
http://crunchbanglinux.org/forums/to...y-lua-scripts/