You can buy a firewire card for your PC - this will allow you to plug a MiniDV straight into the computer. Some Mini DV cameras have external analogue inputs allowing you to transfer direct from Hi8 to MiniDV. You can then use the firewire to edit on your PC. N.B. Some DV cameras use USB. You could buy a seperate convertor unit, but they are expensive, e.g. Hollywood Dazzle at around �300 which plugs into your PC firewire, and will do DV to PC, PC to DV, Analogue to PC and PC to Analogue. It will also work as a standalone unit to convert between DV and analogue if you don't get MiniDV with an analogue input.
Some DV cameras come with video editing software. But if you're looking for a more professional product, something like Adobe Premiere is one of the best, but costs a couple of hundred of quid. Some verison of Premiere come with their own firewire card. These can be useful, as the extra hardware on the card can speed up the process - e.g. If you add fades and wipes to your footage they need to be rendered before they can work, a dedicated card can do the effects in real time, making your editing much quicker.