Jakob,
I would assume that JNet could run on Windows 8 since SAPGUI 740 can be installed on it. I am running Windows 7, so I'm not 100% sure.
If you would like, I can send you a link to download the SAPGUI740 installer and the JAVA JRE 7 installer. If you are interested, send me a direct message and I will provide you the link.
-Jayson