Well, rendering is a three or four fold problem with computers. Cutters need the best everything to not waste time rendering because REAL TIME needs more and more RAM with each level of video you have. Also, you need a fast HDD to get better playback. The processor needs to be good as well as the GFX card but not to the extent of the HDD and the amount of RAM.
For Rendering, you need as much RAM as you can get so 4GB will do you good as a start (and finish since it's a laptop). You processor is good so no worries about that, but your HDD is slow. You might want to look into getting a portable, FW400, 7200 rpm drive to use as a scratch disk.
macsales.com has some really good ones with multiple ports and you can go backwards down the HDD lineup and get a cheaper 60GB or 80GB 7200 rpm drive.
p.s. only 25 minutes for 3 minutes..... 😀 I wish. http://www.youtube.com/watch?v=7K__bxZpRpU every 10 seconds took about 15-20 minutes. At the end, my cheezy but wonderful MacBook Pro Core 2 Duo couldn't even convert it to 8bit NTSC for final output. Had to convert it to normal DV. (yeah... I know... it's a cheezy promotional video 🙄 )