Your footage should be importable into his editor since he's already editing in HDV. AVCHD is a format that all the popular NLE's support. As far as mixing the formats, I don't think that would be an issue. It would seem like any clip that can be imported onto the timeline in either format is then editable.
Give me about a week and I'll verify that and post here. I shoot HDV and my buddy just bought an HF200. We plan to experiment with storing his AVCHD footage via my netbook onto an external HDD for an upcoming trip later this week so I'll grab a small clip and see if there's any issues mixing the formats - I use Vegas MSP.
The simplest way would be to get a external SDHC card reader and exchange SDHC cards. You can transfer the contents of the HFS-10's internal flash drive to a removable SDHC card within the camera. Or shoot directly to the external card. You'll want class 4 or higher SDHC cards to record AVCHD cleanly.
btw, the Pixela s/w that comes with the camera is junk. Even Canon says so. My buddy was having all kinds of import problems, Canon USA recommended he just import directly to his editor (Pinnacle Studio 12) instead. And you may need to upgrade your NLE version. I used Vegas Movie Studio - for SD it was fine, for HDV/AVCHD I needed the Platinum version. Pinnacle Studio is similar, you need the middle package for AVCHD.
Also computer upgrades to edit in AVCHD, it has higher requirements than even HDV. Somewhere well above the minimum requirements specified otherwise it won't transfer cleanly and you may experience frequent lockups.
You could also copy the entire directory structure from your camera to some type of external storage via USB 2.0 which he could then import from. This will be quite a bit slower though.
