Need a MBP Storage Solution

I'm a PC user converting to a MBP for a HD video creation in FCP, I'm going to be producing video from 5-30mins in duration (these files in final form could be up to 100MB each), the hard drive space has me worried about getting a MBP vs. a Mac Pro tower. I've been told to have a scratch space, and I'm guessing that the hard drive native to the MBP is best used for applications and the os, creating a gap on how to have a scratch space separate without getting latency or delay innate to an external drive......can someone recommend a solution to my problem that won't leave me wondering why didn't I get a Mac pro tower? I've seen posts that recommend a p2 drive but, I'm not sure how that works, is it an external drive that acts similar to a native drive to the machine? Is there latency with this option? Also it looks like p2 interfaces only hold 60-100GB, I was looking for an external option in the 1TB space, is this just not a good architecture that I'm looking for? I'm trying to find someone that can convince me that I don't need to storage drives on a mac pro, that I could be just as well off with a MBP with a reliable external drive that doesn't lose me a lot of time in latency in writing to the external