Open iPhoto in both accounts.
Make sure sharing is turned on in Preferences.
Click on your shared library in the source pane on the left in your husband's iPhoto library.
Drag and drop.
Sorry to leave out a few steps earlier!
You can actually log in to multiple accounts at the same time using a feature called "Fast User Switching". You can enable it in the Accounts panel in System Preferences. After it is enabled, you should see a menu in the top right corner of the menu bar that will allow you to switch to a different user account without logging out of your account.
After it is enabled, you should follow the following steps.
1. Open iPhoto in your account.
2. Check the Sharing tab in iPhoto preferences to make sure that sharing is turned on.
3. Use the Fast User Switching menu to switch to your husband's account.
4. Open iPhoto in his account.
5. Make sure sharing is turned on in his iPhoto preferences.
At this point, your library should show up in the source pane on the left. Click on it. You should see your photos and be able to drag and drop them to his library at the top of the source pane.
I hope that is a little more clear!