scvroadie

Just purchased a pair of speedplays, for my wife. She currently has on her bike the cheap Shimano SPD's. I know there are several different methods to determine cleat placement on the bottom of the shoes. What works for you**********

San Rensho 

I install the cleats and tighten the bolts enough so that I can still move the cleat relative to the shoe with some resistance. Put the shoes on and clip into the pedals, take feet out of shoes. From here, I adjust the shoe where i want it relative to the pedal, fore/aft, sideways etc. When I have the adjustment I want, I rotate the pedal so I am looking at the bottom of the shoe and I outline or mark the cleat relative to the shoe. Take the shoes out of the pedals, line up the marks and tighten.

i_r_beej

Many bike shops offer fitting services-- whole bike and/or cleat fitting.

I went to a LBS and had a cleat fitting (i had suffered some overuse injury during a recent double-century) and it was extremely worthwhile. They charged about US$150 for whole bike and US$65 for cleat.

I discovered that i had my cleats positioned too far back and my toes pointed too far inward. My feet also rolled to the outside. After the fitting my feet are positioned with heels inward, and my feet are positioned "asymmetrically" with one heel farther in than the other.

Now i ride centuries pain free! Amazing. Best 65 dollars ever spent!

So i'd recommend that you check around for fitting services. Very worthy investment.

HillRider

If your wife is comfortable with her SPDs, install the Speedplay cleats so the pedal spindle in in the same position relative to her foot as the SPD pedal spindle.

capwater

Inside "bump" just behind your big toe should be directly over the pedal axle. Good starting point.

powers2b

Ball of foot over axle is the norm.
Adjustments follow.

waterrockets 

+1 I've set up a lot of people this way, and they felt perfectly balanced.

I start by putting the shoes on, then placing masking tape over the "bump" behind the big toe (mentioned above). Then, I draw a 5mm dot on the masking tape right where the center of the bump is on each foot.

Next, install the cleats such that the axle mark (if they don't have one, make one) is directly under the dot on the tape for each shoe. When checking this alignment, place the cleat flat horizontally on a counter or table -- this sets a reference for "beneath the dot."

I position the cleat left/right as far in (close to the dot-side of the shoe) as it will go to guarantee no interference with the cranks, but you may want to pull them back out to lower your q-factor later.

Once fore/aft and left/right are set, I tighten the cleats so I can just barely rotate them. Then I sight down the shoe from heel to toe, and rotate the cleat so it's parallel with that sight line.

Then re-check fore/aft placement (this is the most important adjustment).

Remove masking tape.

Tighten every thing down and see how it feels. Adjust as necessary (unlikely). Ride once (normal ride), and tighten cleat bolts again when you get back home.