That would work. Or get a DVD recorder for use with your TV (i.e. like a VCR but it uses DVDs instead of VHS tapes). In either case, record in best quality mode, like 1 hour per DVD.
You will need one extra piece of software to convert the video from DVD format for use with iMovie. MPEG Streamclip + Apple MPEG-2 plug-in for Quicktime, Visualhub, Handbrake, and Roxio Toast are just some examples. This part gets discussed in this forum all the time, so you should be able to find more details.