if you take care of your computer... PC v MAC means very little. However, the following is something to consider:
Macintosh is pretty much tailor made for the video professional. Their laptops are phenomenal, and will run Final Cut Pro or Avid Express pefrectly.
PC is great too... however, you're then excluded from Final Cut Pro.
Basically, here's what to think about when considering this:
#1 - If you're truely serious about being a filmmaker, do not consider I-Movie. The program is designed for the home-video maker... it's for mom and dad to put their x-mas video's and soccer tapes onto a digital medium... some "fancy" editing, and they can feel more special about it... adding music and th like.
#2 - Professional software, even a lower-end version, is a must. Final Cut Pro is great, and so is the low-end version Final Cut Express. Avid Express Pro is great, and so is the low-end version Avid Express DV.
#3 - A macintosh will allow you to select from a number of the best systems to buy... mainly Avid and Final Cut. If you can't afford the full versions, definetly go for the low-end versions.
#4 - While PC will open you up to using something like Vegas... that's likely out of your price range. Also, the PC is rarely set-up perfectly for video on a mac... meaning USB importing.
#5 - Macintosh comes set-up with Fire-wire importing... so you'll be all set to work in DV at the highest level.
#6 - A lot of people will start praising the attributes of "Adobe Premiere." However, you should visit the AVID forum below... where I've posted a beautiful comparison review of Avid, Premiere and Final Cut... to sum it up though... Premiere is nothing more than a glorified home-movie editing platform... it's a RAM hog, and the results never equal the work your computer will do to get those results. It's still a good program... but only when you're restricted to using it. see the AVID forum to find out more.
So, overall, my recomendation would be to buy the Mac.
They're fast, they're made for film & video makers, and they're built to work.
Good luck and happy shopping!