Hi Cornelia,

In general, the laptop manufacturer doesn’t care two hoots about which OS you use and the warranty they provide is limited to the hardware.
The warranty is for the hardware, laptop manufacturers do not provide warranty for the software, so installing the technical preview will not void the warranty however you may encounter some bugs and crashes so don't forget to back up your files and important documents before installing the preview.

However, I’d suggest that your read up what’s written on the Warranty Terms & Conditions document included with the laptop you got.

However you cannot claim warranty for viruses, bugs or software crashes which are caused by software. even if the manufacturer provided you with Operating system, you are referred to Microsoft for such issues.

I hope this clarifies your doubt.

Regards,
Lokesh