Just create your spreadsheet and click on the "Publish" menu, where you will find the option "Embed in Website/Blog". From there, after agreeing on making the spreadsheet public, you can copy the HTML and paste it in your website.
Here is how the embedded Zoho spreadsheet looks like:
And here's the code:
<iframe src='http://sheet.zoho.com/publish.do?docurl=uQcCx5q7c8%2BexjSstIh0sQ%3D%3D&name=W5%2BmaSCODVz%2BuVm31GQvyw%3D%3D'
frameborder='0' scrolling='no'
style='height:500px;width:600px'>
</iframe>
frameborder='0' scrolling='no'
style='height:500px;width:600px'>
</iframe>