So how long is this wall? The short wall has only a single 2x4 becuase
your
rim joist(s?) is bearing the weight. And how long is the total span? And
is this a single joist? Not two 2x12's? Are your floor joists running
the
entire width of the house, or do you have posts in the basement?

There is a large steel member that runs down the center of the house. Based
on the looks of the finished lower level, I think there is a single post
supporting this steel beam, aside from the sides of the house. The wall in
question is about 26' long, with the steel in the center. It's a single
joist - 2x10". House was built in 1980, in case that's relavant.

I'm no structural engineer, but my guess is that the rim joist is load
bearing over that short wall.

That's my concern. If I knew it definitely *wasn't* then I'd feel very
comfortable doing the repair.

I'm anal, so what I would do is put in new (snip)

That sounds like a decent plan, but as usual, there are complications.

I've posted 2 pictures of the situation:
http://www.fischersplace.com/images/...k/deckrot1.jpg
http://www.fischersplace.com/images/...k/deckrot2.jpg

As you can see, the rotted section is directly below the left edge of the
patio door (and it's supporting jack/king studs), and also above a window
below. Unless I replace the entire section under the patio door and to the
right of the window below, I'd have to presumably do some pretty hefty
beefing up of the window header so it could support the weight of the joist
(and deck) above.

What you could do for support is pull off a couple of rows of siding above
the rim joist, then lag bolt a temporary 2x12 to the studs that surround
the
area you'll be replacing, then jack up that 2x12 from the outside. make
sense?

Makes sense, except for the patio door. I'm assuming I can probably jack on
both sides of it, ignoring the span of the door itself, since the structure
above it is supported by a header? What size jacks would you recommend for
this? Would standard screw jaks ala Home Depot work, or should I rent some
beefier ones?

Also, when you put on the new deck a good idea is to shim the new ledger
out
a bit. Cut some treated 1/4"(or less) strips to use where you'll bolt
your
ledger onto the house. Inevitably, water will get behind the deck ledger,
this space will allow for better drainage. Don't forget the new layer of
tar paper over your new rim joist area, then good flashing over the new
ledger as well.

That makes sense, as long as it doesn't violate any codes.

And, of course, you shouldn't listen to any of us. You should call a pro
who
can see it with his/her own eyes

Point taken. Like I said, I'm open to any advice on who to call for
something like this -- even just to get an estimate. But aside from $$$'s
being a concern, I currently have an open sore in the side of the house and
it's been pretty rainy lately -- so I'd like to tackle this very quickly
(aside from me wanting to resume my plans to work on the deck itself...)

Thanks bunches, hope the pics and further detail help diagnose this problem.
I'm also asking lots of questions just so I don't assume (and miss)
something - I hope it isn't making me look woefully ignorant.

-Tim