They will never look as high res as in iPhoto. Video has much less resolution, always, plus less color range and less dpi. Are you looking at this on an interlace CRT monitor? What resolution is the project in, HD,SD,DV? If you wanted to do a slide show with high res look at Powerpoint(yuck!) or Keynote from Apple.
Hope this helps-
Matthew
Dual 500 G4
OSX 10.3.5
Ram 1.38
FCP 4.5/AE 6.5/DVDSP3