Anilrgowda

I need to protect my emails as much as possible and wonder about the difference between PGP, digital certificates and public/private keys.

Which is the most secure? The easiest for a small group to use? How are they related?

How does thawte.com fit in?

soln
The easiest for a small group would be PGP or GPG.
PGP etc is based on a 'web of trust': you define who you trust. This uses self signed certificates.

Digital certificates and public/private keys are part of a PKI: public key infrastructure. It's targeted at larger groups (the whole of world actually). The trusting part is handled by a third party trust authority who creates and signs the certificates (thawte is an example of such a company) on behalf of the certificate requester. That way a certificate chain is build.

I would suggest that PGP is best suited for a known set of users, like you.
Except if you live in Belgium or Estonia. Both countries have rolled out a public eID system, with certificates on the ID cards for all citizens (protected by a PIN code).
If your group is in one of those countries, then you have a PKI system readily available fully integrated with XP, Outlook, but also linux etc ...
Wish the rest of the world follows this. For once I'm glad to be Belgian ;-)