Is 3.3v supplied by motherboards?

["Carey Sasser" <sasser@hp4.nmg.sms.siemens.com>]

I am designing an expansion card that uses a mix of 5v and 3.3v parts. My
questions are:

1) Should I derive 3.3v through a regulator on my board or is 3.3v
available
from the motherboard?

2) If 3.3v is available, is it available on all motherboards or only some? 

3) If 3.3v is available, which type of connector do I use? 5v, 3v, or
universal?

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