The pdf, if you could do it, would be even larger, I suspect, than 400MB. I would suggest copying the images to a USB memory stick, and passing it around.
Alternatively, get a copy of GraphicConverter and use its Catalogue feature. I don't know if you can do similar with iPhoto.
iPhoto has a ability to place many pictures on a page.
Create a new album and put all the pictures you want in there, then select all the pictures and File > Print and select Contact Sheet.
There you will have the ability to Print and when the box appears, choose PDF to the Desktop.
Compress the file zipping it down and stay under the file size limits of your email provider.
Another solution is to host the pictures on Flicker then email the web address to everyone you want, however it's public.
Another method is to use DropBox and email the password for the shared account.