How much computing horsepower do I really need to use iMovie?

Question

How much computing horsepower do I really need to use iMovie effectively?  I'm trying to make a one-hour movie from HD camcorder clips and still images.  My iMac 24 with Intel Core 2 Duo running at 2.33 GHz and 2 GB of RAM severely bogs down and regularly locks up or crashes.  Now that I've painfully managed to insert all of the video clips and still images, my iMac won't play the video back smoothly so that I can edit the work.  Within a second or two, the video either stops or becomes extremely jerky, while the audio continues to play.
Do I really need an $8000 MacPro 12-Core computer running at 3.3 GHz, with 32 GB of RAM, twin, 2 TB hard drives, and a $1000 27-inch Apple display, or will something less costly work fine for producing videos?
Thanks for any advice,
Joe

Answer 1

Thanks for your reply, Klaus1.  I'm currently running Snow Leopard.  I'd considered upgrading to Lion but was told, even by Apple, that I wouldn't be satisfied with its slow performance on my iMac 24.
I have plenty of hard drive space with 160 GB available on my internal hard drive, but I've been storing the archived video clips and the iMovie projects on a fire-wired, external 2 TB drive.  Could it be that using an external hard drive for the iMovie project is part of the performance problem?
A quick check on the Apple website shows that my iMac 24, which was manufactured in mid-2007, can support up to 4 GB of RAM.  I wonder if I should consider a RAM upgrade before upgrading the entire computer.  How big a deal is it to replace RAM in the iMacs?
Joe