Database advice

Hey all, new to this forum...

Spent the past year or so developing small web apps for small businesses using ColdFusion and MSAccess. Recently got a contract for a much bigger job, and I'm looking for some friendly advice.

The job is for a website with a reasonable amount of database work, not too many records for Access to handle. My concern is that the number of users is expected to be very high. I haven't had any problems with this with the apps I've developed, however they've been very small, for no more than 10 users at a time.

In developing for this type of site, what method would give me less headaches? I have no experience with MySQL, XML, or much else, but I'm sure as heck willing to learn whatever I need. Is there a language/DB system that's well-suited for this type of work?

Anything but Access.
I'd go for Firebird or MySQL as you seem to be working on M$ platform, SAPDB is a bit tough for a beginner (don't get me wrong, what I mean is that Access behaves differently from standard dbs, and if you are used to it only, you would face a steeper learning curve) and PostgreSQL support for Windows is beta quality.
Notice that MySQL lacks some sql features that Access has (subqueries and views to name a few), this is not the case for Firebird, SAPDB or PostgreSQL.