Is it possible to replace the dock (but just the dock)?
Unfortunately, No. The "dock" is part of the entire launcher and "home screens". They are, all the "same application". But there are widgets like most of the widgets that HTC Sense has. If you really don't like it that much, you should be able to find replacement widgets for the ones you like that work with other launchers like Launcher Pro, GO Launcher, or ADW Launcher, for example.