Hi
Sounds as if your PC is just too slow to process the clips at the same speed as the sound. What format are the clips? If they are 1920 x 1080 HD MPEG4 you may get it running a bit faster if you convert to MPEG2. or you could try producing a set of proxy clips of smaller frame size and with the same name and location as the originals and use these for the edit and replace them with the originals when you export.
Your problem is also that you have to load all the cips when you load the project and this can take an age if everything is on the timeline. (But note my comment regarding the cache file.)
It may be more convenient with a big project, next time, to load a first group of clips to the media list and edit these, then saving the result as a sequence.
Load a second set of clips...edit them and save as a second sequence etc. This is what Borate suggests.
If you save the project after a sequence is created the time line is cleared and the program will load from the .vpj file faster.
Also remember that if you loaded your project directly into the later version of VP, the cache file would have been empty and it would have taken quite a time to regenerate, hence your 1hr wait. (Won't help the playing speed problem though 
but your work will load faster next time.
Nat