Listen to your body, Fiona. If you have full-blown flu, posting messages on the Runners World forums is as much exercise as you can cope with at the moment. Rest, sleep all you need, take time off work, rest, treat the symptoms with paracetamol, ibuprofe, codeine, or a combination of all of them, and did I remember to mention rest?
You can expect at least a week out of action, although you should be able to do your race. You will lose some fitness so it won't be your best race performance, but forcing yourself to go out training before you're ready is just going to lead to injury and delay your recovery.
I hope you feel a lot better soon.
Cheers, V-rap.