I don't find an easy way to reduce the size of a photo with Picasa.
If you send the email directly from Picasa, it will reduce the photo size automatically.
If you would rather do the reduction yourself you can download the free Irfanview program and use it.
With Irfanview, you open a photo and then at the top of the screen click "Image" and then click "Resize/Resample". That will present you with a page that gives you many choices for reduction size.
I recently bought my first digital camera (Canon A610) and have been using Picasa to edit (am loving both of those). Right now when I attach a photo to an email it is *gigantic* (I think you know what I'm talking about- you scroll to the bottom of the email to see a nose, scroll over to see their eyeball), how do I go about making it smaller on the email? I'm exporting the photos from Picasa to My Pictures and attaching to an email from there.