Hi Jim,

I suggest you get a kit with 2 stands, 2 monolights and 2 umbrellas.
Something like: http://www.alienbees.com/digi.html

For a single portrait set up one flash high, aimed at subjects face,
max power, and well to one side of the camera. Put the camera on a
tripod, so the lens is even with the subjects eyes.  Set the other
flash close to the camera, but on the other side of the camera from the
first flash.  This flash should be at lower power than the first and at
camera height.  Adjust the power of the flashes so the side flash casts
a triangular shadow of the nose, and the flash near the camera fills
that area in so it isn't too dark.  Since you can experiment for free
with your 20D, you don't really need a flashmeter.

Also see:
  http://www.photo.net/photo/studio-photography
  http://www.google.com/search?q=+portrait+flash+tutorial

Good luck!

Peace,
-chasfs
http://chasfs.com

Diff. strokes, and all: I'd be inclined to not invest in fixed strobes,
unless you are sure you'll stick with studio type photography, and
instead get the 580EX and one of the smaller but new Canon flashes,
which would obviate getting the transmitter for less than a hundred more
than the transmitter, and gives off light as well as triggering the
slave. My understanding is that the two flashes can be both used in ETTL
mode, with one stopped down to act as fill or secondary light, but I
haven't done that yet with my 550 and 580. I was even considering
getting the 430 or 200 something to mount on the camera, to trigger both
the others, but haven't yet.

Do you have a decent flash currently?

If you go with studio strobes then it's very hard to set up flash
lighting in the field.

If you go with the 580's then you can use them either in the studio or
out in the field - score one for the 580's.

Studio strobes don't work with the camera's E-TTL flash metering - so
it's "manual all the way" - score two for the 580's.

You can get inexpensive brackets that allow you to beam a 580 into an
umbrella on a tripod - the only downside is that the 580 on the tripod
must be able to see the 580 (or speedlite transmitter) on the camera -
inside it's not such an issue as the signal will bouce around the walls
quite nicely, but outside (especially if you've got an umbrella between
the transmitter and receiver) then you'll likely strike problems.

By the way, the speedlight transmitter and the 580 used as a
transmitter (master) communicate in different ways - the first via
infra-red, the 2nd via the pre-flash. For this reason a 580 used as a
transmitter generally has a better range.

With this in mind, you'll now understand why the 580 zooms to 24mm as
soon as you switch it to master mode. Additionally, if you set the
custom function on the master 580 to tell it not to fire, it still
fires the pre-flash (this one has people scratching their heads a bit).

For what it's worth I've now got 3 580's (heading towards 5 all up) -
great units.

The 580ex makes a very compact flash system that will fit in your bag.

I would suggest buying proper studio flash with a modeling lamp. You are
working blind with flash units like the 580EX et al.

Very good portraits can be done with a single umbrella and yield very
good results.  Better is to have two umbrellas with two lights.

A basic two light portrait setup can be done with flashes set to manual
power levels, not TTL.  This will aid in consistent exposures across a
bunch of shots and clothing changes.  It helps to have a flash meter to
set the fill and key light but with a digital camera you can "converge"
to a proper setting with a few test shots.

It's 'better' to use studio strobes such as AlienBees, but a couple high
end speedlites are just as good.

Good camera stores usually have a variety of brackets to mount your
camera flash on a stand with an umbrella.

The most basic setup is for the fill light to be near the camera and
shining down the lens axis towards the subject.
They keylight usually above shoulder height and at an angle to the lens
axis (30 - 60 degrees).

Avoid key or fill lighting from getting at the lens

The key light should expose whites as white and the fill light should
expose whites as greys.  Set each light separately.  The more "grey" the
fill light, the greater the key:fill ratio.  Whites should not be burned
out.

If the key light is half the distance to the subject as the fill, and
they're both at the same power setting, then you will have something
close to a pleasing basic portait lighting ratio.

IMO the better umbrellas are the "shoot through" type, not the refelctor
type.  You can usually pick up some shootthroughs at a used camera shop
or swap event for 5 - 10 $.

For about $40 you can add an AC strobe to put behind the subject and
light up the background.  Backgrounds can be overlit by up to 2 stops or
underlit by a stop or more.  With an AC strobe and an old can, a spot
can be projected on the BG to backframe the subject.

Antother $40 and a rim or hairlight is made...

(Note: these lights slave off of the master, so in digital TTL/preflash
they will fire on the preflash.  You need to fire the master in manaul
mode with all lights at manual power levels.  Note that this, once set
up, leads to consistency in exposure).

Have fun.