Well, it's normal for large apps like iMovie and iDVD to take 4-5 seconds to open, partly because all the data needs to be loaded from the hard drive. Even if you max your RAM to 2gigs for a few thousand, you'll notice a difference of maybe 2 seconds. You can get 7200rpm hard drives now for laptops (almost 2x what your laptop hard drive is now), but they're pretty expensive and can't hold as much as the lower-rpm hard drives can.
I guess the bigger question is why do you care? It's a few more seconds to open a program, and even if you shell out big bucks it'll reduce the time by a few seconds.
My suggestion is just live with it unless it really bothers you. More RAM will reduce it by 1-2 seconds maybe, but it isn't really worth it considering the money you'll have to spend.
Cheers,
m1k