I almost forgot:

question:
Can I make voip calls on the N800 (like skype or using a SIP based provider)?
answer: Skype will be released in june for the N800, so untill that time: no skype calls on the n800.
The N800 includes a Googletalk client by default, but it doesn´t have a universal SIP client. Gizmo project is an application that you can install, that includes a partial SIP client with limited options (not all SIP services work when using Gizmo), in addition to Gizmo project Voip services.

question:
what is the webcam quality like?
answer: terrible, absolutely terrible. ANY webcam you buy for the PC will have a better video quality (even the $10 ultra cheap ones),
The webcam is totally useless currently: only the google talk client can start video calls, but the Nokia video call client for the pc is rather buggy, and very few people use google talk anyway.
Because of the low quality picture, you don´t want to use it for video recording or for use as a digicam.