I am planning to buy a spyderpro from colorvision to cal. my LCD monitors (for photos).
I learned that they can use it cal. the projectors too.
I searched the web and see some people do similar things.
However, I just wonder what is the best way to do so.

1. Set default settings on the projector. And use this to cal. the HTPC's output.
2. Use some cal. disk to cal the projector first. And then use this to cal the HTPC's output.

I think option 2 should be the better choice. Is it true?

Yes, #2 would be the better choice.
Use HCFR to calibrate your PJ, then the spyder software to make a profile for it.