You can use the Media browser in iWeb to drag an iPhoto album to your Photos page. However, you cannot select and drag multiple albums (using Shift-click or Command-click). If you want to add several iPhoto albums, you must add them one at a time. Each Photos page can hold up to 99 photos.
Note: You can add photo albums to iWeb pages other than the Photos page, but pictures are easier to organize if you use the photo grid on the Photos page.