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It is depending on the app you use as to how intensive it will be on your CPU.
Other than that, as long as you have a firewire interface for your inputs, pretty much the minimum spec MB or MBP would have no problem handling it, but may get a tiny bit of lagging, which if you find is the case, you may want to upgrade the amount of RAM you have. I would upgrade RAM after your purchase from OWC or Crucial, as you will find it cheaper than you will from Apple.
As for the Hard Drive, after market with OWC or Newegg once again is the way to go.
The faster HD may be a little noisier (not noisy, just noisier), but that shouldn't effect your recordings as you wouldn't be positioning your microphone over the HD
I used a 2.2GHz Macbook with 2GB of RAM before I got this 2.4GHz i5 MBP for single and multi track recordings, and never had a problem. On the MB I had a tiny bit of lagging, but not noticeable enough for the untrained ear.
Using Logic and any MBP you will no doubt be happy with the quality, but as I would recommend to anyone, the faster the processor your budget will allow, is the MBP to go for.
Edit:
As much as I would recommend a faster HD, I would also recommend a large HD (min 500GB with plenty of space), and an external firewire HD for mass storage.