Wich pgp is supposed to be stronger, 2.6.2 or 2.6.2 i?

What are exactly the differences between them?

I'm not sure what you mean by "stronger"? I must admit that I have not taken a close look at 2.6.2i, but my understanding is that it is an internationalized version of code similar to 2.6.2. The keygen routines, RNG, and IDEA code are the same; the RSA code is different, but supports the same range of keysizes. The difference in RSA code has to do with US patent law, where PGP 2.6.2 uses RSAREF, so it is licensed to do RSA. Other than that, I doubt there is any real difference. The major crypto and security functions are the same (or should be -- as I said, I've not taken a close look at 2.6.2i). -derek