You will need an analog-digital converter like the
Canopus ADVC-110. They accept the analog signal from your old camcorder and convert it to DV (digital) so it can be used & edited by iMovie and other software.
Many miniDV camcorders can also be used as a converter, if you have access to one you can use. It has to support a feature called 'analog-digital passthrough' and most miniDV camcorders do.