Copy the qtcurve.dll to the folder Psi+/styles (pre-creating the appropriate folder styles in a folder with psi.exe).
Start the Psi + one of the commands:
Qtcurve style
psi.exe -style qtcurve
Plastique style
psi.exe -style plastique
Cde style
psi.exe -style cde
Motif style
psi.exe -style motif
Cleanlooks style
psi.exe -style cleanlooks
Oxygen style
psi.exe -style oxygen
CleaRlooks style
psi.exe -style cleaRlooks
How to run Psi+ by command with key?
Create a shortcut to a psi.exe, in the shortcut properties to register the command after the quotation marks (example: „C:\Program Files\Psi+\psi.exe“ -style oxygen) and run the Psi+ by this shortcut.
Create a bat file or cmd file (an example of content: start psi.exe -style oxygen) and run Psi+ by this file.