If I use my work computer from my home wireless network, will they be able to see what I access from my home computer using the same wireless network?
EDIT: I seem to have possibly misread the question (judging from the upvotes I guess I wasn't the only one). If you're using your work laptop at home, it's very unlikely that they'll be able to see anything on any other machines on that network. There are ways of doing it, but nothing that's very likely to be in practice. It's not something I'd worry about.
Original answer follows the break, which is the case for things you do ON the work laptop at home.
It's possible, yes; it depends on what they have installed on the system and what level of access they have to your account. It's entirely feasible that they have something running that logs every single keystroke you make and saves it for later review. It's even possible they have monitoring software installed that will allow them to see what you're doing in real-time without your knowledge as long as you're online. (You could probably block this stuff from your home router but that would require some foreknowledge of what it is in the first place.) If you're browsing through a VPN, they can VERY easily see everything you're doing internet-wise.
It's also entirely feasible that they couldn't care less, but I wouldn't risk my job over some porn. Keep your work assets for work use only.
That would require some sort of sniffer that records all packets. The home PC would not route traffic through the work laptop so it is unlikley the work admins would have access to your traffic.
They may have acess to the stuff you do on the work laptop (as noted by @Shinrai ) but the home one would be a challenge.