Companies reserve to themselves the right to check the usage of the laptop they gave you.
In some countries they cannot do it without actually informing you about it.
In any case they may be able to check what you did with the laptop they gave you.
It should be written in your company's employee guidelines what's allowed and what is not allowed... if you follow the guidelines you always on the safe side.
The real important bit is to know how much leverage you have for it.

Most of the companies do not care if you skype with you gf, or read books, or watch movies on such machines.
Most of the companies don't give really a damn about what you do on those laptops until there is an internal investigation or they want to fire you.
Only at that time they get interested.
Guess you are going to have to go old school and pay for your porn..
not necessary... for most of the setup, you can always run the browser in "incognito" mode, maybe from a USB and you should be safe.
For extra safety a software like
http://www.sandboxie.com/ may help