coverchicago,
I use an Panasonic AG-HMC40 and it works great with FCE v4. Using Capture & Log within FCEv4 works great with AVCHD media content. Also, you can directly transfer AVCHD media files directly to your hard drive for editing without using FCE Capture & Log. My next statements are based on the assumption, you have never used FCE, so if you have FCE experience, please forgive me. Its hard to tell what experience a forum user has when asking a question...
As the other folks have indicated, only use your iMac's internal drive (1TB SATA Drive) for loading your applications. For Example, I use a 1TB LaCie external firewire drive (1394 FW-800) for my FCE files disk (capture scratch - where you ingest your AVCHD content, FCE AutoSave Vault files, FCE Thumbnail & Waveform Cache files, FCE Render Files, FCE Audio Render Files, etc.), a 1TB LaCie external drive to store my third party media (overlays, effects, graphics, Sound Effects, Background Music, etc.), and a 1TB LaCie external firewire drive (FW-400) to store my final rendered projects). Don't use your internal drive for saving FCE project files (.FCP files), capture media, or third party media, only because you don't want to "thrash" your internal drive with loaded down large media which will eventually get removed, repeated, and removed again, as projects start and finish.
Once I finish projects, I can clean my external FCE files disk, as needed, then reconfigure through FCE Preferences and Project Setup without disrupting my internal Mac OS drive. It will save you a potentially expensive disk lesson down the road and prevent "slowdowns" on your internal applications drive. Plus, if you ever have a system problem, simply unplug your external drives before repair or reload. Your projects and media are protected. There are some really good books out there which explain sound disk setups for Final Cut video editing. Lastly, get you a free copy of Carbon Copy Cloner (CCC) for backups or if you ever need to clone and restore a drive. Its a great addition to the Disk Utility in the Mac OS. Good Advice whether you are editing on a Mac or Windows platform.
Good Luck!
WBMP