I'd mainly need it to store files on, shift files from and to my external HDD (USB 2.0), use Microsoft Office and perhaps Photoshop and/or other photo editing tools. But photo editing isn't a requirement since I'd prefer to do that on my Desktop.
It doesn't have to be fast at all, as long as it's got enough processing power to do the things described above...
I've been using laptops longer than desktops. Laptops are hindered primarily by their slow hard drives, 4800rpm or 5400rpm. 7200rpm 2.5" notebook drives were recently introduced.
To meet your requirements, a PII-300 or greater with 256MB RAM, a 14.4" TFT screen @ 1024 x 768, would be more than adequate. Altering screen resolution from "non-native" results in a slightly fuzzy image. USB 2.0 and ethernet did not show up until P4 laptops. Some laptops do not use mobile processors, they use desktop processors. They get extremely hot and have short battery life. Look for Mobile Pentium or Pentium-M.
Any laptop manufactured 1999 or later will meet most of these specs. Compare prices here: http://www.dellauction.com