Boot Method on OQO02, what option is this?

I was trying to reinstall the OS on my OQO the other day, and I found this option in BIOS by surprise.

Looking at the “Boot Method”, Boot Sector, which make sense for Windows.

Booting by Windows CE??

Looking at the HTC Shift UMPC, which dual-boot Windows Mobile 6 Professional and Windows Vista, I wonder what this option is for? XP Emb? Windows CE.NET? Windows Mobile?

Do you know more about this?