If you go to this page: http://www.adobe.com/products/premiere/
And click on the Buy/Upgrade link it appears you can upgrade from any version of premiere. But a quick call to Adobe Sales wouldnt hurt to confirm.
Did you find out we if you can do it
It does look like you can I've just been trying out the trial
And I think I want to buy it does anybody know where the best place is to buy it
Are they doing any promotions
Any promotions will be listed in the Buy/Upgrade area of the Adobe.com Web site. Other than anything listed there, any additional promos will have to be through a certified reseller.
The Premiere Pro User Group is probably the least updated user group on the entire Internet. That being said, there is a promo code for members of the user group. It's substantial.
Thank you. That is good to know.