Download speed slower than Upload Speed

(This is a new question about a different Verizon DSL line from my previous posts about DSL vs cable.)

I'm working at another location now which has Verizon DSL. The speed of uploading files via FTP is 200-400Kbps -- slower than it should be, but fine for what we're doing here. However the download FTP speed varies from 15-35Kbps, way too slow for most work. Verizon DSL tech came out and checked -- the upload speed on the Verizon side of the box was 500K, but the download speed checked out at 1.5M. This location is 2-3 miles from the Verizon central office.

My question is - why is the download speed fast and upload slow? Could this be due to something on my end? modem, OS, internal building wiring? OS is Win2000.