A LOT. The hype and tech demos were enough to make people believe that the PS2 was going to be on another level compared to the Dreamcast.
We also had some interviews stating that they used data from the CG movies to make some of the tech demos such as the Final Fantasy 8 demo and the old man who was based on a model from Spirits Within.
If I recall correctly I think George Lucas mentioned something similar about using data from films to the PS2.
While the DC was demonstrating the incredible visuals of Shenmue and the character facials, the old man tech demo obliterated anything seen on the DC, including Sega's Irimajiri tech demo.
The DC looked like old news.