Know: I know nothing (and I don't even come from Barcelona!
).
Think: The rumour was that Montoya would be joining McLaren in 2005
and that Williams had already signed his replacement.
If this is true, the only driver I can see Williams having signed up this early is one who started his F1 career at Williams and who now drives for BAR. And I don't mean JV...
I'm not sure myself that JB would be the right man at Williams, but Sir Frank seems to think highly enough of him, and he's better placed than me to judge, so why not.