I don't know what software you were looking at, but I'm on a Mac and have no problems with my 705. But I've never been able to download a map from Google Maps to anything, or had much success creating maps on Google Maps when I didn't want their auto-routing option.
Are you looking for street maps (there is a freeware option, but I really haven't investigated it, because Garmin and Navteq have their copyrights for a reasonand I don't want to be out in the middle of nowhere with an untrustworthy map), or routing?
You can download a .gpx or a .crs directly from MapMyRide to your 705. I don't use courses at all (actually, people report fewer problems when they use courses, I just haven't bothered). To download your route, choose Route>Save to GPX>Download GPX, then choose folder Garmin>Garmin>GPX. Then when you're ready to navigate it, choose Menu>Where To?>Saved Rides, select the ride you named, and choose Navigate.
Make sure you have Auto-Recalculate set to Off or Prompted.
ETA: I haven't updated my maps yet (actually I'm waiting until next year, since there's been some major road realignment in my area that wouldn't be on this year's maps yet). I initially bought the bundled unit. But you have to actually buy the City Navigator disk to have integration with Training Center (if you use that). It's a little bit more involved, I believe, since I think you have to call Garmin for an unlock code once you've copied the maps from the disk to your chip - I'm 99% sure you can do that, but be warned that I haven't tried it. Still, City Navigator 2010 is available in DVD for Mac or directly on the micro-SD card.