take a look at this site:
"SQL Server Express and Visual Web Developer provide a simple integrated platform for building dynamic and reliable Web sites. "
If you reach the 4 GB limit, you can upgrade to SQL Server 2005 Standard. When you put the standard version on a web site, you'll probably want the 'per processor' license, which currently runs at approx. $5,000.
Take a look at this FAQ's by mrdenny faq962-5153
If/when you need to upgrade to standard, you'll need to either uninstall express, or install standard as a named instance. If you un-install, you'll need to detach the database first. Then un-install express. Install standard, and then attach the database. If you install standard as a named instance, all you'll need to do is to detach the database and attach it to the standard instance. Then, of course, you'll need to change the connect string so that your app connects to the named instance (running sql server 2005 standard).
Your bigger issue will be converting the database from Access to SQL Server. While the syntax is similar, it is NOT the same and you should expect there to be a fair amount of work involved.
My suggestion would be to install SQL Express, convert the app to use it, making sure you test ALL areas of functionality.
-George
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