GT200 taped out 1.5 months ago
According to Dailytech GT200 taped out early March. This term means that the GPU-designing part would be pretty much over and they would start to make these chips. They also said that they have had ready GT200-GPUs ready for few weeks [testing + PCB design].

This would mean that Nvidia would be ahead of schedule with GT200; their original roadmap said that GT200 would be launched "Fall 2008", but now it looks more like "Summer 2008". They also said that they would present this next gen at Computex [June 3.]

They also said that Nvidia would start to phase out 9800 GTX and GX2 as early as next month..to make room for GT200.
DailyTech