I have a work laptop and wireless router (Draytek) that supports VPN. To access work files I need to launch the VPN on my laptop with a password. My private PC is hard-wired to the router. Can work see my private files and internet traffic with no software installed on the private computer regardless of split-tunneling set-up on the router or not?

To be sure that no one can see your private files from anywhere, disable file sharing, set Windows to ask for a password after it boots, use mac filtering on the router and change the default password to the router. You are limiting yourself to preventing someone from seeing your files from the other end of the VPN but not from the router which is a lot easier. The steps I mentioned prevent both.

thanks guapo, I have very little network / router nowledge. I have taken your advice and turned off file sharing and creating a windows startup password under the administrator. I do not know passwords for the router as work set it up so cannot change these or tell whether mac filtering is on. Does this mean that when I surf the internet this doesn't go via the work server on my private computer? It would go via my normal ISP? My company monitor internet usage times; I work from home so in the past if during the day I have need private internet access I have used private computer thinking that work couldn't tell. Could they have?! By implementing part of your changes (router excepted) am I now reasonably well protected? Thank in advance.

Meant also to say that I'm not sure whether the router was setup to split-tunnel. Will this make any difference to reply?

It's not the router that determines split tunneling, it's the VPN. For example, when my girl friend connects to her job through the company VPN, she can't print to her LAN printer.

so if the VPN determines split-tunneling and my private computer doesn't have VPN installed on it, internet usage goes via the ISP and not work's server?

Correct, the internet usage on your private machine has nothing to do with the VPN.