Slow transfer speed...temp fix but why?

[CALAMIKE]

I have been battling this problem for weeks. I have a HP pavillion ze4325 notebook and a Sony DVD writer DRX530UL. I have gone thru several PCMCIA USB 2.0 devices and they all seemed to work at full speed sometimes but most of the time the max write rate was .3x to .4x.
By accident I discovered that any motion on my screen..like dragging a window back and forth while writing..the speed would jump to 4.0x..and in fact if I just have windows media player playing a song while writing..everything is fine..if I pause the media player..the write operation immediately goes down rapidly. This is also true for the on board usb port even doing a simple file transfer via drag and drop to an external hard drive...same thing speeds up dramatically when media player is playing (with some sort of video motion). Using the same external hard drive connected direct with a PCMCIA adapter (not usb) this phenomenom does not appear...writes and reads at normal speeds. So problem seems to be in USB and oh yes firewire also. I forgot to mention that monitoring the cpu useage it goes up dramatically like from 6% to 60% or more when I do the media player bit or just drag an icon or window back and forth on the screen. So my question is whats happening here and how can I write at normal speed without doing this. Sorry for the long post it is my first and I am very frustrated...Thanks for any suggestions.
(P.S.>>>my OS is XP Home sp1 and the adapter I settled with is an Adaptec AUA-1422 duo-connect)