Sorry y'all. I've been working on other things for a bit ($work/2, A fence, a LAN party, and a busted Lada Niva mostly).
Using dlltool to create the library files from the definition files seems to have worked. Gtk2 seems to be working and I'm just about to start working through the Gtk2-perl tutorials and stuff.
I've noticed that a lot of you also seem to have the Perl source available (which I don't) and I'm wondering if getting that set up to compile makes a difference. OTOH it's a bit out of the scope of this project which is specifically about using Strawberry Perl 5.10 and what it provides (which seems to be enough).
My final conclusion is that Strawberry Perl does provide everything you need to compile modules, provided that they don't need more libraries. Almost everything I've done is telling the compiler where these external libraries are. I haven't yet figured out if this is a deficiency in the Makefiles, or in the way that minGW is set up in Strawberry Perl. Both seem equally likely.
My next steps will be to rewrite this as two more meditations (one on setting up a complier, another on compiling Gtk2-perl) as this has kind of turned into a "How can I X with Y and Z?" kind of problem. I also think I need to set up minGW from scratch so that I can get a better understanding of that process, as I suspect as most of my problems could be made to go away with a reconfiguration script. I may also have to look into ExtUtils::MakeMaker.