Moving host - database questions

[30et]

Hi all
I am moving my vbulletin to a new host.
I have copied the php files and am now going to copy the database.

If I copy the database and then change the DNS record to point to the new host, then the old database will probably get new posts etc which the new database won't have because of the time for the name server to change.

Is there a way to compare the two databases and update the new database with any new posts from the old database? I think this wouldn't work because the new posts will have unique keys etc which will be already used in the new database.

Another question is how should I transfer the database. Its 1Gb so I don't want to download the whole thing to my local computer then upload. I know how to use SSH and SCP and TAR on the old host. I was thinking there would be a way to use 'mysqldump' to backup the database to the new host. But I am not sure what the syntax is. I found this

$ mysqldump foo | ssh user@remote.box.bar.com mysql foo

where 'foo' is the database to copy. But I am not sure how to enter the username / pwd in this command for the local database user.

Any advice would be appreciated.

Thanks!