Well, here's where I am today with this.
I tossed out my other attempts and started again but using my 2012 Anvil version and installed it into an XP bottle. I then installed a .NET framework into that same XP bottle, stopping it after the completion of .NET4 (letting it run into the installation of 4.5 seemed to cause the whole thing to fall into a loop from which it never escapes).
Since I had already placed my gdiplus.dll into the Windows System 32 folder as explained by the previous poster here, I had only to enter the Wine Configuration utility for my fresh Anvil 2012 bottle and 'Add' gdiplus.dll, then 'Edit' this to run 'Native' (instead of 'Native,Built In').
The end result is that I now have a functioning version of the basic Anvil Studio (Yayyy, Yippee!).
Flushed with both relief and victory, I attempted to install my previously purchased plugin packs, Combo Pack 1 and the Print Sheet Accessory.....
UNFORTUNATELY...trying to install these addon packs so far has proved difficult...impossible even for now.
Because they are .exe files I must run them like any other installer, but even when I try to install them into the same XP bottle that houses my main Anvil program, they stop as soon as they start, with an error message that states "Anvil must first be installed before this pack can be added".
I have tried various combinations of steps to install these packs but so far, no luck.
Has anyone had any luck with this additional step?