Kirk's advice is sound for when you are going enter the same data for a lot of images at the same time -- select all the files you want to update, press CTRL+I, enter the IPTC values you want (make sure the check box is on for the fields you want) and then click "Apply Stationary".
Now, if you are going to update each photo with unique data (say, a competitor number or a name), then the flow is slightly different. I do a lot of this with my sport event photography work -- updating IPTC data for 2,000+ images for a 600-800 person 10K run is not unusual for me. I set all the "common" IPTC data values during the ingest process so I don't have to fiddle with it later. I then go to the first image in the contact sheet, press "I" (not CTRL+I) and get into the individual image IPTC mode (this is the one with the image shown on the right side and the IPTC data on the left). You can then put your cursor in the field that you want to update with the competitor number and navigate to each image using the buttons under the image or the associated short-cut key. Something I didn't notice until the last release was the ability to click on the photo and enlarge it briefly so you can look at the image closer to get the competitor's number or name. By using the short-cut keys (ALT+[ and ALT+]), you can leave your cursor in the field being updated and then as you move from image to image, you don't have to grab the mouse to put the cursor back where you want it -- it stays in the field being updated. Once you get the hang of this, you can fly. I regularly do 900 to 1,200 images per hour and hope to see that improve even more with some shortcuts in 4.5.2.
Once you get the competitor number in the file, it is simple to them update other fields using IPTC Code Replacement files, but I recommend mastering the rest of IPTC first, then moving to Code Replacement.
Another piece of advice is to sit down first and make an IPTC metadata strategy. What data are you going to store in which fields? Sure, location, city, state, country, caption, etc are all obvious. However, if you are shooting sports, consistently putting the game name, event code or name, competitor number, competitor name, etc., in the same fields from event to event will REALLY make it easy for you to find a photo in the future. I still have customers asking about photos from an event I shot in April 2006 and I can find their photos while I am on the phone with them and make the sale. I can do that because I *KNOW* the class or division name is in Supplemental Category 1 while competitor name is in Supplemental Category 3. The overall event name is always in Source. Others will have a different strategy, but the key is HAVING a strategy and sticking to it. There is profit in that kind of discipline <grin>.
Good luck,
-Mike
