scary database prefix on upgrade warning

I ran zc_install to upgrade the database.
I read the following halfway thro.

"Change Database Table-Prefix
If you wish to change the database table prefixes, enter the
new prefix below.

NOTE: please verify that the
prefix name is not already used in your database,
as we do not check for such duplication.
Using an already-existing table prefix will corrupt your database."

Well I wouldnt want to corrupt my database, and it uses zen_ prefix on the tables, so what happens when I use another prefix?

I have downloaded the database tables, so if I create another database
without the prefix, how do I then reinstate the database?
Sorry if this a bit garbled, but Im new to this sort of thing.
Any help appreciated
cheers

I apologise for posting this in the wrong forum.
Ive put the query into **Upgrading from 1.3.x to 1.3.7**