importing from pgp 6,5,8 - web of trust

[Pieter Thysebaert]

Hello, 

I'm new to gpg, switching from pgp.

Suppose I am user "A", and I have created a keypair (using pgp).
I've also added user "B"'s public key , and have signed it with A(all using 
pgp)

Now I would like to convert all this to gpg.

So I --imported my (=A's) public and secret keyring, and imported the trustdb 
using lspgpot (as in the FAQ)

Ultimately, my goal is to fully trust "B" so I can encrypt stuff destined to 
some user "C" whose key has been signed by "B" without warnings/interactive 
yes/no questions etc.

However, at this moment I'm not even able to encrypt something using B's 
public key without being warned:

2048g/1E7B05B8 2000-12-08 "B"
             Fingerprint: FEDA CB8B E491 4F13 FE6B  0B3D EB2E 0414 1E7B 05B8
 
It is NOT certain that the key belongs to its owner.
If you *really* know what you are doing, you may answer
the next question with yes

The keys for A and B show up as (using --list-sigs)

pub  1024D/E729C33A 2000-12-08 A
sig        E729C33A 2000-12-08  A
sub  2048g/42C18BEB 2000-12-08
sig        E729C33A 2000-12-08  A

and

pub  1024D/C12C6B68 2000-12-08 B
sig        C12C6B68 2000-12-08  B
sig        E729C33A 2000-12-08  A
sub  2048g/1E7B05B8 2000-12-08
sig        C12C6B68 2000-12-08  B

This is what --edit-key has to say about A 

Secret key is available.
 
pub  1024D/E729C33A  created: 2000-12-08 expires: never      trust: f/u
sub  2048g/42C18BEB  created: 2000-12-08 expires: never
(1). A

and about B:

pub  1024D/C12C6B68  created: 2000-12-08 expires: never      trust: f/q
sub  2048g/1E7B05B8  created: 2000-12-08 expires: never
(1). B


So I have B's key signed with A, I have fully trusted B but gpg is still not 
able to calculate the validity of B's key ('q').

In other words, what have I forgotten that will make the 'q' (as in trust: 
f/q) transform into something more trust-ish ?

Can someone help me?

Thanks

Pieter