We're not being unfriendly, but I doubt any of us will have experience of this. Having said that, I would expect that if you are just invoicing the company and not joining them as an employee it would be normal EU rules - you pay taxes in your own country unless you are on site for more than 90 days in one year.
The best thing would be to seek legal advice from a tax professional in your own country to start with.
Tks Jim, I know you are not being unfriendly , I'm just a bit stressed because I'm going tomorrow.
Anyway, that was helpfull, I think it works like you said. Someone there told me that because I'll be using theyre room and computers I had to pay taxes there, but I think that's nonsence. I've asked already to a tax professional here in Port. But I'm still waiting for his reply. When I know something I'll post it here, maybe it will help someone.