When I switch on my new PC, it's so fast compared to the old one that Grub is up and displayed before the monitor has even come on. If I want to boot a live CD/DVD there is no time for me to get it in the drive. Other than repeatedly hitting the Del key on the keyboard as soon as I power on the PC, to get the BIOS setup (then exiting without saving), or just ignoring Grub, sticking the DVD in, and hitting hard reset once the DVD is in, is there something I can type into the command line from Grub that will boot the DVD drive from there?

What kind of PC do you have ?
Mine is rather quick ,but a with separate power cable for BOx and the monitor.Intel Dual Core 1.8 GHZ 2 GB RAM
So I switch on the monitor first and than the system box
First boot device is standard set to DVD
Time enough to open the DVD to insert a CD or DVd in it , because as I said first boot device DVD set in the BIOS set up

No, my monitor powers up when I switch the PC on. It does have its own power cable, but although the standby light flashes when the PC is off, the monitor tube (it's CRT) doesn't power on till the PC allows it to. By the time the tube starts displaying stuff, Grub is already on....

It's a minor thing, but if there is something I can run from Grub's command line to avoid doing a reset, it would be nice...

Not from the grub-prompt.

Hit an arrow key at the prompt - it will then wait for ENTER and you have time to put the DVD in.
and/or then just CTRL-ALT-DEL to do a reset
put the DVD in the drive before you reboot - and set the PC BIOS to boot from CDROM first

yes please.

Leave your bios to always boot cd/dvd drive before hard drive.
If you have a bootable linux usb stick then change that to
usb
optical
hard drive.

Ah, I didn't think of Ctrl-Alt-Delete - I thought that only worked for anything in Windows.

I already have my BIOS set to boot DVD first - if there is one in there.

Thanks for the info.