The primary difficulty here is that, like all of the game mods and utilities, VST is fan-created and not supported by LDW. The original creator of the VST (Borg) relied on the .NET framework, due to the programming environment that he uses. He's using his own computer and the tools that he has available (if you do a little reading in some of his posts, you can get more of the background). He has no Mac and no ability to modify VST to be more easily ported to Mac.
Others, including NP, have looked at creating a Mac version, but have run into obstacles and/or circumstances that caused them to abandon the work. I highly doubt that anyone in our current community here will take up and finish the project.
You could probably use VST (the parts that don't interact with the game) in an emulator, as long as you are using an Intel Mac (since Windows computers and Intel Macs are the same Endian and can both read and write the savegame files correctly). Files created on a Windows computer are not compatible with Power PC Macs. If you opt for this approach, you do have the issue of making sure that you're being careful with how you handle the savegame files to prevent total data loss, however.
Another solution is to use either Boot Camp (a free, built-in dual-boot solution for Intel Macs) or a virtualization product (such as Fusion or Parallels) to run the Windows version of Plant Tycoon along with VST in a 'native' Windows environment. I do all of my development work, as well as most of my testing, on a MacBook Pro running VMware Fusion. It's a very elegant way to run Windows and Mac OS X "side by side" (in a manner of speaking). It's a magnificent way to "have it all!" and doesn't require advanced juggling skills in this situation.
