The first gen Intel CPU (core duo) is significantly inferior to the Classic MBP Penryn. CPU aside, the x1600 GPU is also significantly inferior to the 8600gt GPUs found in the penryn line. The combination of the two represent a vast improvement in performance from the first generation Intel MBP to the current Classic MBP (penryn). Remember, though, the first gen Intel MBP was released over 2 and half years ago - a long time when talking about changes in technology.
As far as heat is concerned - there is most definitely a noticeable improvement from the Core Duo line to the Penryn - but in my opinion, there is still an issue with heat.