Hi. First of all, I hope you know what you're doing, here.

Going from SQL Server 2000 Standard To SQL Server 2008 Express, might not be a good idea.

I expect that you've done your homework on the limitations of SQL Server 2008 Express.

As far as I know, as long as you're using SQL Server 2008 Express, no servers or CALs licensing is required.

Try to talk to the Microsoft's SQL Server Sales department to get it cleared up.

Adieu!