yes it can be done and will work fine if your internet connection is good enough. It will work the same as if the internet connection goes right into the PS3.
Search around a bit and you will get the info you need for your setup, this is normally referred to as Network Address Translation (NAT), although I *think* in some places you will see it being described as internet connection sharing. This process is the same for any type of computer..so you won't need to focus your search on PS3 specific ways.
I would only recommend going down this route if you are quite familiar with computers/networking or know someone who is........as with anything about networks, if you run in to problems it can be tough to find out whats going wrong.
In short what you want to do is:
0) Plug an ethernet cable between them
1) give your laptop NIC a static IP
2) give your PS3 NIC a static IP (not the same as laptop of course)
3) Configure the connection sharing -> you'll need to turn on NAT/connection sharing - google how to do this for whatever OS is on your PC. Its probably just a single option.
4) In the NAT options, you need to define the ports the PS3 uses for incoming connections (about 2-4 numbers). I forget what they are off the top of my head but can get them later for you if you're stuck.
Once it is done once, it will work for good.
As I said, if you know someone who knows their networks get them to do it - they will be able to do it in 5 mins for ya.
Let us know how you get on,