I wouldn't do a damn thing, if you trust the utilities to protect their systems (which I would, and I'm an electric power engineer who has worked with utilities extensively). You also have the issue that, if the utilities don't protect their systems and the solar storm is strong enough, you'll not have power for a while afterwards (if you believe the alarmists, years), so it really doesn't change all that much if your computer is working...

The worries about a solar storm are very different from the worries about something like an EMP triggered by, for example, setting off a nuclear bomb in space. An EMP is a very short, but very intense, pulse. It won't burn down transformers, it'll kill electronics.

A solar storm is a slow phenomenon that induces high voltages/currents in multi-mile long power lines. That has the potential to kill things like power transformers. Your in-house electrical wiring is way to short to have a significant impact - any solar flare big enough to matter here would be big enough to pretty much heat-fry earth, in which case, again, your computer's survival doesn't matter - you won't survive.

If you're paranoid abut the utilities not protecting their systems, you can turn off the main breaker and you'll be safe. Or run your house off a whole-house backup generator, if you have that.

-- Catull