Upsizing to SQL Server
Access is not truly meant for concurrent use. Microsoft made it easy to use Access over the web so that small companies who couldn't afford (or were intimidated by) SQL Server would have some database platform to use for their LANs (great way to sell more copies of the higher-end Office package, as well). Unfortunately for Internet developers, Access does not handle more than a handful of simultaneous users very well at all. So if you've got a family site that only your friends and such are looking at, Access is probably fine. For anything more than that, you'll probably want to use SQL Server.
QuickerSite v1.6.8 is compatible with SQL Server 2005. Microsoft provides an upsize-feature in Access. It only takes a minute to upsize the QuickerSite.mdb Access file to a SQL Server database. You may want to check Microsoft's Knowledgde Base regarding this topic.
If you want to upsize earlier versions of QuickerSite (v167 and down), you may want to contact me regarding a few small changes to the datamodel.