"you can supply parameters at runtime. The Default Value combo box supplies several options, including [QueryString(arg)] and [Form(arg)]. Select [QueryString(arg)] if you will be supplying the parameter at runtime via a querystring item."
However, it wasn't made at all clear how you would do this in practice, I know what forms and querystrings are but at first I couldn't fathom how you are supposed to pass these parameters to the Web Part. Also, it is not clear whether you can use web part connections (i.e. a provider web part on the same page) to supply the parameter to the consumer web part at runtime. I would have thought this is the ideal way to use dataview web parts without needing to do any coding?... so I started to do some digging.
So then I have discovered 'Insert | Form | Form Web Part' in FrontPage which looked promising. I put one onto the page and made a web part connection to my dataview web part with the following settings
Source Web Part: Form Web Part
Source action: Provide Form Values To
Target Web Part: [my dataview web part]
Target action: Modify View Using Parameters From
...and it just works!
NB: After much tearing out of hair I also discovered this article, which states that you need to enable update support before you can used Stored Procs in FrontPage
