In Gmail or Google Aps, click on the Calendar link top left of the screen to display your calendar. Then if you look to the right you will see a link for settings, click on this then click on the calendar tab.
Next click on the calendar name in the window and the page will refresh and it will have some options for you to fill in. Ignore all these and look for the section that is titled Embed This Calendar. In here if you look next to the picture of the calendar to the right you will see some code, copy this code and paste it in to your page.
When you post the code in to the page make sure you are in HTML mode (click the HTML tab), click save and your calendar should appear like this
If you find that the calendar is not quite the right shape for your theme, just go back in to the page to edit it and look for the bit in the code that says width=”400″ height=”300″ and alter these to suit. The defaults are 800 x 600 so try and keep the ratio the same so it looks nice