This sounds like a problem with your OS in general that is preventing things from working correctly. Probably your best bet going forward would be to back up your stuff and do a clean install of either Windows 7 or Windows 8, depending on how you feel about them personally. Anything would be better than Vista these days Then, before plugging in your Wacom, install the drivers. Should be all set in that case. Drivers also exist for Ubuntu/Linux if you're into that sort of thing that would depend on your software of choice.
If you don't want to update the OS then you're going to want to find a Vista install disk and run a repair install. That should clear up some of the missing .dll issues. Then I would suggest uninstalling anything wacom and going into the device manager and deleting any generic 'HID tablet' drivers that Windows installed by default. Then install the lastest version of the Wacom driver, plug in your tablet, and hope for the best. Running something like piriform's ccleaner might help too.