first survey the different isps that cover your area click here and look at what people have said about them perhaps here in consumerwatch. The minimum equipment needed will be an adsl modem most of which have a usb connection. If your pc is really that old you may not see a great deal of improvement in speed although you should. If you are looking ahead to perhaps getting a faster pc and possibly then keeping the old one as well. You might consider an adsl modem/router which could allow more than 1 pc to connect. The details of what is provided by the isp should be on their sign up page. You may also consider fitting a network interface card which is pci and would then allow rj45 patch cables to be used giving flexibility. These are available for about £10.