Two things come to mind.

First off. The use of USB devices is based on the ability to supply power to them. To properly supply power is to have each connected usb device supply their own power supply. If not then a drain upon your computer power supply is an issue that will cause imminent failure. The sony you noted is an internal drive...so you must have it inserted in a USB external case of some sort. Is it self powered?

Are you using a hub...then try to use the ports on the computer itself and see if it has the same issues.

Also the difference in using a laptop with a minimum power ability over the use of a desktop with a full power supply will make a big difference in what you are trying to achieve.

While you mentioned the XP and SP3 you failed to mention if the USB connection is USB 1.1 or 2.0 which will also cause an issue when dealing with a coupled high end components trying to work at the same time.

I would reccomend that you update the USB driver in your system and see if that makes a difference.

Xp has always had an issue with too many installed drives not being reccognised or failing....this is due to the assigning drive letters to the drives.
A work around is to re-assign drive letters to installed hardware drives....I assign my optical drives letters from the back of the alphebet...x,y,z, and this allows new connections to occupy the lower assignments.