Here is my personal experience (and, I am a full time laptop editor).
Chip: Intel Core 2 Duo.
Memory: At least 2GB
Graphics card: You NEED a dedicated card with preferably, 256MB memory.
Hard-drives: I would recommend getting a 7200rpm internal drive
External drives: I would recommend picking up an eSata ExpressCard slot and using eSata drives.
Screen-size: Variable
Over the past couple of years, I have tried a LOT of laptops from different manufacturers, but have hated all of them, primarily due to their poor reliability. I have been using an Apple MacBook Pro for the past 8 months and it is honestly the best laptop I have purchased. (PS: I run Windows on it)
My other recommendation would be picking up an HP machine.
The above should easily fit into your budget. (If your stated price of 3500 is in USD)
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