I've upgraded my Windows Vista system to SP2. And now I find that Interent
Explorer won't work. In fact anything I run that has a link to the interent
isn't working. My network connection is fine. Any ideas on how to fix this?

Presumably you mean you fire up a web browser and cannot connect to the
internet but can connect to other computers on your network?
I suppose that is not impossible but seems unlikely.
If that is the case then under tools/internet options/connections click the
setup button on the top left.
If you still cannot connect to the internet try resetting your router
(unplug, count to 5, replug). Vista wireless connections to routers are
stable on some machines but very tenuous on others running similar hardware.
At my house two wireless Vista units never drop their connection to the
router but a third periodically requires the router be reset although the
other two units have stable wireless connections.