Weld a steel circle along the undercarage.

Thus encircling the engine, I assume.  But, the wires, tubes, mounts and things would stick out from the engine to the rest of the car, thus breaking the circle.

If you welded on a circle large enough to encompass the whole car, then you may indeed block out magic.  However, a magic user in the car would make the whole construct moot at best.  Circles hold magic in just as well as they hold it out.    Anyway, parking would be hell.

cybrgrl

You know, I wonder if wireless/bluetooth keyboard and mouse would work through a summoning circle. you could shield the pc, but still surf the web using the easily replaceable keyboard and mouse.

Ha!  Good idea!  I think it might work because we've seen devices that rely on a wireless signal work from within a circle (Dead Beat).  Woo!  You may have come up with a way for wizards to use computers! 

Now, I expect you would go through a LOT of keyboards... but consider the possibility for voice recognition software...

Here's the thing.  I'm a computer programmer.  Have been for over a decade.  That means that I not only am familiar with computers, but that I often have to "think like" a computer.

Wouldn't that suggest that I might think "Gee... I should be able to enchant my computer to protect it from magic, no matter what my teacher says."?

I have the impression that you can't put wards on technology.  I imagine that the magic involved in either the act of creating the ward or the functioning of the ward itself would mess up the technology.  If it could be done, I would have expected Harry to put wards on the Blue Beetle by now.

If understanding the technology mitigates the disruptive effects of magic, then we must ask what level of understanding is required?  Would you need to know the tolerances of all the transistors and wires, the circuit board design, and so forth?  If so, then very few people could reach the level of understanding necessary to safeguard even simple modern technology from magic.

However, you could put your computer in a circle (see Dead Beat), maybe a permanent one such as the summoning circle in Harry's lab.  That would let it function even with a strong magic user in the room, but wouldn't let the magic user sit down and browse the web.

No ,but I would love to see a story-heavy single-player RPG like SW:KoTOR or an adventure game like Still Life based in Harry's Chicagoland.

I second that.  SW:KoTOR, VtM: Bloodlines, and Bladerunner would all be excellent role models for a Dresdenverse single-player (or small network) game.

As far as MUDs (ah, found memories of IgorMUD!), MUSHes, and MMORPGs, take a look at this little gem:
http://urbandead.com/
A web/text-based MMORPG!

We do know that the more wizards there are, the less likely technology is to hold out. (SK)
We do know that technology shorts out in the presence of just about ANY supernatural occurance, even if wizard's aren't involved (FM, SK, I think it's mentioned in GP)
We do know that the emotional state of the wizard seems to have some effect on whether the technology will work (Several books, the best reference is DM).
We do know that if lots of magic is flying around, it's more likely that technology will fail, and that mages can focus their hex to some degree.
We do know that magic's effect on technology can be warded against and spells can be used to mitigate it. (DM, DB)

This indicates to me that the effect of magic on technology is a direct result of magic itself rather than the magician.

Bravo, LogosInvictus.  Your post sums up my understanding of Dresdenverse magic, right up until the "As to why" paragraph.  I don't know why magic interferes with technology.  The books give examples but no explanations for magic's effect on technology.  Therefor, I suggest leaving the matter open - not publishing one reason in the RPG that might conflict with future Dresden File books.  To address the issue, you could include a sampling of theories presented *as theories*.  GMs and players could use one or more of the theories as they see fit.

My favorite theory is that magic messes with probabilities.  Fits all the facts in the books so far.

cybrgrl

Intimidation (threats, scaring people, provoking anger, interrogation)
"Don't hurt the little coroner, gentlemen," the man said.  "We'll need him.  For a little while." Dead Beat.

Performance (playing to an audience, artistic composition and appreciation, creative communication)
"I'm, not going to let the Jolly Rogers laugh at me like that.  I mean, come on.  Five guys named Roger.  How much polka can be in their souls?"  Dead Beat.

"Great entrance.  Love the hat." Dead Beat.

Scholarship (mundane research, sciences, languages, using computers
"There was only one file on the jump drive, and it was empty.  The only information on it was the
file name, and it was just a number." Dead Beat