I have no problems using Premier Elements 4 (nor with and Photoshop Elements 6.0 too for that matter).
When I first started using Premier Elements 4 I thought it had major unreliability issues with Vista x64, but soon found the kind of problems I was having were down to the source video format rathert than the OS. (XP users were reporting the same.)
Basically, if you have too many source files in a project it can just fall over due to all the resources it needs for positions, clips, effects etc. (Maybe your problem is similar.)
I ended up following a recommendation on one of Adobe's forums to convert the project sources to MS DV AVI format (which you can do through Premier Elements itself by "Save As") before adding them into a project. A bit of a pain - but don't have any problems now.
Hope you resolve your problem too.