I have Pentium 4 system 3 GHz, 1 GB RAM ..... (no built-in WiFi)
I installed Ubuntu 12.10 on my PC, works fine.
It picked all the drivers for audio, video itself.
I plugged TP-Link 54Mbps High Gain Wireless USB Adapter (TL-WN422G) ..... (link for the device: http://www.tp-link.com/en/products/details/?model=TL-WN422G)
Now what happens is that the WiFi network is detected and shown in the "Network Connections", and it is also connected to it but when I open Firefox it is as if there no internet connection at all.