Help with working with color and profiles

Like many others, I suspect, I am having trouble managing the colors on my iMac to match the prints I get. I have a few questions, but first, some background:

1. Screen calibrated with Huey Pantone. Calibration was done with monitor brightness all the way to lowest. I don't use Shades or anything else. I have my Display Profile set to this profile. I'd be happy to post my .icc profile if I knew how. I can email it to anyone who can help here.

2. I have been sending my prints to Costco with the option of turning OFF their Auto Correct. To try to get things to match, I downloaded Costco's printer profiles from http://www.drycreekphoto.com/icc/Profiles/Minnesota_profiles.htm#MN (Eden Prairie, Glossy and Lustre paper profiles).

3. I shoot photos with a Canon XTi with color space set to sRGB. I am using iPhoto 08.

So here are my questions:

1. I loaded the Costco printer profile icc files into /Library/ColorSync/Profiles/Displays. When I open ColorSync, I see them under Profiles/Displays. However, in ColorSync/Devices/Displays/iMac, when I go to change the profile, I navigate to these files but the computer just beeps and won't take them. I thought all icc files could be used by monitors and printers - can these Costco iccs only be used for printers (I noticed the Costco files are 4MB, the other display iccs are 4KB)?

2. How does iPhoto handle color spaces? I import my photos off my CF card. Under iPhoto / Prefs / Advanced, I have both Copy Items and Embed ColorSync Profiles checked. Which color profile is it embedding? The one from the camera (some generic sRGB) or the one my display is using (the Huey)?

3. As a test, I exported my photo as a full size TIFF (a 3.3MB jpeg became a 28MB tiff). I opened the TIFF in Preview. Preview / Tools / Assign Profile came up as "Camera RGB Profile" (so I think this answers question 2 but I'm not sure). While in Preview, if I now change the Display Profile (from Huey to Adobe RGB), the whole screen changes, including the photo I'm looking at in Preview - shouldn't Preview hold the photo the same since it's using a different color profile?

4. I set the Display Profile back to Huey. In Preview, I go back to my photo and under Tools / Assign Profile I assign the profile my Huey profile (instead of Camera RGB). I save this as a jpeg and reimport into iPhoto. When I compare these two photos side by side in iPhoto, they look indistinguishable. Why, if on the original import iPhoto embedded the Camera RGB profile into the photo and I make a copy assigning the Huey profile do they look identical? There's no reason to assume that the Camera RGB and Huey profiles are the same! Or is it some trick where the Display Profile is overriding everything?

5. Lastly, I reopened the original TIFF export in Preview and assigned it the Costco profile (happened to use the glossy one). Lo and behold, what appears on the screen is a much closer version to what I got back as a print. Finally, as one last tweak, I changed my Display Profile from Huey to Adobe RGB and the picture I saw in Preview was closer still to what I got back from Costco. I changed the Display back to Huey, kept the Costco profile assigned and saved my TIFF back to a JPEG. I imported into iPhoto and compared - it looks much closer to my Costco print.

So I'm utterly confused. How do professionals manage their color workflow? Is my Huey calibration whacky? Why, if I assign a color profile to something in Preview, does it really depend on what Display Profile I have set (I thought profiles managed color, but it looks like it's relative).

I apologize for the rather long post, and very much appreciate any help and suggestions here!

Thanks!