I have a friend that recently started using Ubuntu, and I've been answering his questions via the internet. However, I'm stuck on this one. He bought Linksys WPC11 wireless card, and says he was able to create a network connection, but was unable to ping or use a browser. I'm not quite sure where to start in figuring this out--what are some common causes of this sort of problem?
Basic Network Diagnostics:
Since your friend says she/he has network connectivity you could skip steps 1 & 2.
If step 3 works then she/he has internet connectivity if it fails check out whether the default route points to his/her gateway (eg: use route command and look for an entry without a * as the gateway)
If step 4 fails then she/he and has not setup DNS and cant perform name translations.
These basic steps should be enough to identify the issue.
Depends on how he configured things, but you might see if he can ping an internet server by IP instead of name. Perhaps he didn't set DNS servers -- or specified bad or invalid ones.