According to my laptop it's in "Non-free (Official2008.1-9)"
I guess if you used One as the install medium it won't be in.
Any road up, have you set up the media manager? Also, have you use this:
http://easyurpmi.zarb.org/old/
This is great for setting up repositories. You might want to set-up the PLF stuff too.
When you get to step three, open a console, go to su, highlight the text in the box on the website below where it says "Type this in a console as root" and click the middle mouse button in the console. This will paste the highlighted text and load up all the extra repositories; when it comes to the last one, you'll need to hit enter.
Once you've done that just type in at the command line (might as well as you're already there):
urpmi wlwifi-3945-ucode
(You can always go back to MCC to add the package if you prefer.)
Hope that makes sense and helps.
Edit, just seen someone say it's in the Contrib repository, which I'm pretty sure you can do from Media manager in MCC.
