After reading some of the documentation and the website page about SATA, I got the software working by doing the following.
Make a bootable USB with SpinRite. This is via the "write to disk" feature. You can install it on a USB stick with a DOS format, and it shouldn't delete the existing data (but back it up anyway).
Boot the E6410 and press F2 to get into the setup. Look for the SATA settings in the second category. Set the mode to ATA. SpinRite 6.0 works only in this mode.
Plug the USB flash memory in, and boot. Press F12 to get a boot menu. Select USB.
Booting will be quick. Start the program and do what you need to do.
Once SpinRite has started, you can remove the USB drive.
Why boot from USB? Because the Dell E6410 doesn't seem to boot from CD when it's in ATA mode.