m4him,
Almost certainly this is a driver problem. To work well with MJ you need to get the Rio drivers installed that come with the MJ Plugin. If XP has already installed the drivers that come with it, I would suggest that you remove them fully by following the directions at
http://www.sonicblue.com/support/rio/default.asp?menu=support&submenu=Legacy_Rio&item=faqs&product=Rio_500_PC#20399Also uninstall the Rio Plugin for MJ. Make sure your Rio is disconnected and reboot.
After you reboot and BEFORE you connect your Rio, download the MJ Rio plugin. When you connect your Rio and XP asks if you want to install the default drivers, DO NOT accept the default, instead, point the installation to look in your System32 directory where it will find the drivers that we distribute with the Plug-in.
After this, you should be set. If you are still stuck email me at steve @ jriver.com.