Here's a small trick that confused me for a while this morning.  VSeWSS creates a setup.bat & .wsp file that will deploy a site definition into a specified server.  Running setup.bat from the command prompt appears to be the obvious way to do that.  You can also override the default web and site urls, e.g:

setup /weburl http://myserver /siteurl http://myserver

The default being localhost (or whatever you developed against).

However, this was failing for me becuase the specified web did not yet have a root site collection and some part of the site definition (web parts) were scoped to the site.

The solution is to create a blank site using stsadm thus:

stsadm -o createsite -url http://myserver -ownerlogin administrator -owneremail me@myemail.com

Then you can deploy the site defintion using setup.bat. When you browse to the new site you will be prompted with a list of possible site definitions.

Like all things SharePoint this is easy and obvious when you know...