> 1. Could I install Firebird2 64 bits on a database server and access to
> the database from 32 bits web application on another machine?

Yes.

> 2. What is the process to convert Firebird 1.5 database to Firebird 2
> database?

Make a backup on the old (FB1.5) server. Uninstall the old server.
Install the new server. Restore the backup on the new server. Check all
of your functionality for new bugs.

Upgrading from FB1.5, you need to deal with the fact that the old
TIMESTAMPs only used seconds precision while they use miliseconds in
FB2. Some language constructs which were valid (though suspect) in FB1.5
no longer work in FB2 (e.g. duplication of columns in INSERT, and I
think in UPDATE too).

Josef