All the big software companies have HD capability. Avid has a bunch
based around DS Nitris but that;'s a really high end system, costing
hundreds of thousands.
FCP and Avid Xpress Pro support Panasonic's DVCproHD codec, either from
the camera or as an offline codec (ie you'd have to recompress the
Adobe they are the ones ahead of the curve with HDV having just bundled
cineforms ConnectHD plugin to new copies of Premiere.
On PC, Canopus has it's Edius suite which also comes with realtime
hardware options, but then you're adding thousands to the cost. Apple
can handle HDV but not in realtime, so you need a programme like
LumiereHD to convert to DV or DVCproHD for realtimte editing, you can
then later reconnect to your original HDV files, of course this adds
hours (possibly days) to your editing workflow compared to native HDV
editing like Cineform or Canopus offer.
Right now, PC platforms offer more speed and flexibility, but the Mac
option could be cheaper. If you offline cut in DV then you could on the
cheapest eMac available.
Cost has very little to do with the choices right now.