As of a couple of weeks ago, you're no longer going to receive crucial security patches and Hotfixes from Microsoft. Is it worth the risk? As to the wireless problem, your PCI card might be old enough not to be able to recognise WPA and in that case, you might need to go down to WEP. As that is so easily hacked, you might consider upgrading that wireless card
I do not have sp3 and don't want it if i can help it.