SQL server vs. ms access

[Bryan H. Davidson]

I've got a quick general question that I'm hopping someone out there might
be able to answer.

I've done a great deal of work using MS Access as a web application back-end
and have seen dynamic / static hybrid sites run efficiently that receive up
to 40,000 + hits per month.

What I'm having a hard time finding documentation on is, at what number of
simultainous users does Access break down?

My second question is, by simply migrating an Access database to SQL server,
will a web site then automatically be able to handle high numbers of
simultainous users? Or is an overall redesign / reindexing involved in order
to truly optimize a database?

Thanks

Bryan H. Davidson
Electronic Products Librarian / Web Master
University of Arkansas Libraries