I have a three PC and one siffy connection. All three PC connected to Hub. I want to connect all three PC to Internet.

You should have 1 router to share your internet. I hope you will have IP and DNS from your ISP. You can create the DHCP in your router.

Hope you OK

Regards,
ABB

Try adding another network card in the PC which you have given the sify connection and share it through internet connection sharing ( I hope you know what is internet connection sharing process) then for the remaining two pc's in tcp/ip properties give the option as obtain automatic ip . Its finished

Both answers are correct. However a router will give you a more stable and faster connection as well as a more secure one.