Unbearably slow transfer rate. Any help welcome.

So I'm backing up about 139 gigs of data from one external hard drive to another. I'm copying from a Seagate 2TB drive via USB to a WD 2TB drive also connected via USB. It took one hour to copy the files to the Seagate drive, but when I start copying from the Seagate drive to the WD one, I'm told it'll take 39 hours to complete! I did the math with how fast it's actually running and I'm getting a transfer speed of one Megabyte per second! So my questions are...

What the heck is going on here?

How can I get it faster? Preferably without spending any money on other software and/or hardware.

And now for some obligatory information!

-Both hard drives use an external power source

-I'm using a Mac Pro tower with a 2.8GHz Quad-Core Intel Xeon processor

-I have 4 GB of 800 MHz DDR2 FB-DIMM memory

-The Seagate drive is capable of USB 3.0, but the tower only has USB 2.0 (I know it just means I'm using USB 2.0, but my point is that drive isn't just slow)

-The WD Drive is only capable of USB 2.0

-Both drives are formatted Mac OS Extender (Journaled)

-One drive is plugged into the front of the tower, the other is plugged into the back

-Currently, Activity Monitor says I'm only using 1% of my computer's processing power

-Nothing else is running (except Firefox right now, but it's still at only 1% usage)

-Three other things are using my USB ports, a keyboard, a mouse, and a printer (the printer isn't even on)

-I have one FireWire port, but the hard drives can't use FireWire anyway

-I'm backing up from a separate computer so the files are not on the tower and there is not enough room for them on the tower (I cannot copy to the tower from one drive, then copy to the second from the tower)