Here is how it works for me, its painful and it really upsets me having to do it this way... I think Nokia should get this working as a main priority, anyways...

FIRST SYNC:
Enter the usual params (m.google.com 443 secure connection etc)
If the process gets stuck, just open your n900 browser and go to https://www.google.com/accounts/DisplayUnlockCaptcha
Enter the captcha code, submit
Start the sync again.
In advanced settings/calendar choose 'create new'
It should go all the way through the first import.

After that, the normal sync update does not work, so I set it to manual sync (not automatic sync)
whenever I want to sync I have to go to the address above, unlock the captcha, then go to the mfE settings and trigger a FULL RESYNC

I didnt find any other way around and I have no idea of why this works.. its cumbersome and annoying but at least it works...

hth
sergio