Best Editing SW for Specific Needs

Having found iMovie to be a blunt tool for my video editing needs, I am trying to determine which option would be lowest cost for my particular needs. My editing needs are as follows:

• Video Lecture with Overlays. I need to tape lectures then be able to EASILY overlay the lecture with photos or video clips while the lecture sound continues.
• Music Video. I need to select a piece of music, then tie images to specific points of time in the audio. I need to assemble photos nonlinearly then apply transitions without everything shifting around.

I view Final Cut Express and Premiere as my options.

Having spent a LOT of time playing with iMovie HD 6 and the 09 version and finding their logic frustratingly backwards for my needs (lay down video then lock audio clips to it; apparently needing to separate audio from video then reassemble to do overlays), I'd like to avoid expensive and time-consuming experimentation that might only lead to disappointment.

Any help would be appreciated.

Keith