Excellent! I was able to get this working as well, however at XMPlay's Options and Stuff window, after selecting "Winamp VIS Wrapper - MilkDrop 2.2 (off)" and clicking the "Config" button, I get this:
Microsoft Visual C++ Runtime Library | Runtime Error! | Program: C:\Program Files (x86)\XMPlay\xmplay.exe | R6034 | An application has made an attempt to load the C runtime library incorrectly. Please contact the application's support team for more information | OK
After clicking OK, I get a "Winamp Vis wrapper" window with the MilkDrop v2.22 plugin highlighted and I'm able to click the Start button and make it run.
I'll say also that to use MilkDrop v2.22 I simply removed the 2e version DLL from the directory, replaced it with the 2.22 version, and did the mt.exe command. I used the msvcr90 dll copied from Winamp's MilkDrop installation of v2.22.
If anyone has an idea to fix this, that'd be great, otherwise I think the vis plugin is functioning as expected, and it's awesome to watch.