PSPvideo9

This might be because the program is still not completely compatible with windows 7. I checked the windows 7 compatibility center and it said that "information is coming soon" which means that the company and microsoft are testing the software or something. There are definitely a few areas in which vista MIGHT be faster than windows 7. This is due to the fact that windows 7 allocates the resources in a smarter way.
This article provides a lot of information about graphics in windows 7:
Engineering Windows 7 : Engineering Windows 7 Graphics Performance
Quoted from article:
Certain trade-offs had to be made for the desktop responsiveness improvements which benefit a wide range of systems. For example – the elimination of the duplicate system memory copies which “speed up” certain operations introduced slightly reduced performance as the CPU now has to read data back from the video memory. An analysis of real-world application statistics showed that these operations were rare. However, certain GDI micro-benchmarks which issue these operations show some performance degradation. This is something to note if you are running existing benchmarks that stress specific GDI operations repeatedly, which isn’t necessarily a reflection of real-world performance. Our observation has been that these slow-downs do not impact the end-user functionality directly and that the memory savings directly result in Windows 7 being much responsive overall. The improvements overall are definitely noticeable on memory constrained PCs with shared memory graphics.

Thus, it is possible for windows to be slower on intense operations like converting video. However, the awesome thing about windows 7 is, that the operating system, while performs the job slightly slower, will be more responsive throughout the entire operation. This is due to the 1.1 wddm drivers that use less memory and less resources.

Personally, I prefer the style windows 7 has....If this really really bothers you, try using another converting program or wait until this program is checked by microsoft for compatibility issues.

Regards