it does tell you in the manual that you can connect the 2500 to the pc and transfer files that way, so well done for finding that!
however, what it does not tell you, is that the USB1.1 spec is very slow! to do 20GB of samples, would take you ages man, not worth it, get a usb2.0 laptop hard drive enclosure, just for the initial download of the 20GB it'd be worth it!
here's a rough estimation:
USB1.1 allows a maximum of 12Mbits/second that means 12 million bits.
there are 8 bits in 1 byte.
in 20GB (gigabytes) there are (20,000,000,000 x

= 160,000,000,000 bits
so:
160,000,000,000/12,000,000= 13,334seconds
which is roughtly 3.7hours! that is a 'best case' scenario, so you've been warned!
ps you could just leave it going overnight i suppose.