Its actually pretty simple.
No need to install cinepak codec, virtualdub can deal with it by default.
Just open the file you want to convert (this is the part you may need to install a windows codec or two for), then select the video compression, select cinepak, then adjust your audio to suit (eight bit mobo is probably a good idea for a slower cpu). Adjust your color depth to sixteen bit, then save as legacy avi.
That's all there is to it.
Im not infront of my windows machine at the moment, so I couldn't remember menu names, etc., but with the above description and even a little bit of computer literary you'll be good to go

To be honest, having to have a look around the software a little will better help a person to learn than having their hand held all the way through anyway. Besides that, it really is very simple once you have the basics.