John,
Just create separate pages for each set of photos using the Photo page template - you can have as many photo pages on your site as you want. Then drag any pictures from the iPhoto section of the media browser onto the picture placeholder on the photo page.
If you have a few photo pages you'll probably then want to create a separate photo index page. Create a blank page to use as your photo index. On this page, create links to each individual photo page by dragging a relevant picture from the media browser. Click the picture and set the 'enable as hyperlink' in the Link tab of the inspector and choose the relevant photo page in the drop-down list of your pages.
If you create a photo index page, you probably won't want the individual photo pages shown in the iWeb navigation menu - just un-check the "Include page in navigation menu" option on the Page tab of the inspector.
You can see how I did it with my Holidays and Photos pages at
http://www.dai-towell.net
That's it! Hope that helps.