USB Hi-Speed Problem

I have a Sony PCV-RS404 PC, 3Ghz Intel Pentium 4 HT, ATI RADEON 9200 Grphics card, using Windows XP Home.
My external devices won't run at full speed because, although the PC has 6 USB2 ports, it tells me that they would run faster if a USB 2 enhanced HI-Speed was present.
I have gone through every possible method within Device Manager to try to fix this problem, to no avail.
I have an LG USB 2 DVD writer, a Western Digital Storage drive plus scanner etc., and a little dialogue box creeps in to inform me that I need an Enhanced HI=SPEED host controller.
Any help please?
jonjon

 

This may clarify the problem for you:

http://www.microsoft.com/whdc/system/bus/USB/USBFAQ_intro.mspx