The Vostro 2420 came with Ubuntu 11.10 out of the box, and when I installed Kubuntu 12.10 I lost wifi. So I found this solution and followed it and got wifi working. Now I just upgraded to Kubuntu 13.04 and wifi no longer works.
lcpci shows the following: Broadcom Corporation BCM43142 802.11b/g/n (rev 01)