Cyberlink PowerDirector, Pinnacle, and Nero all work acceptable with avchd.
They are entry level but they seem more suited to this difficult format
than Premiere.
I use NeoScene from Cineform in order to transcode my AVCHD footage from a Panasonic HMC-150. I am on a Mac and therefore using that version but there is also a PC version. My understanding is that CS4 support is coming soon. I currently use it with CS3 without any problems.
What camera and what version of Vegas 8 are you running. Although they are terrible at playing nice with others, Vegas usually is pretty good at playing nice with its own camcorders.