On most PCs it is possible to set the boot order at the BIOS level, without
the need for pressing any extra key along the way later. That "press a key
to boot from CD" sounds more like some special bootloader or other software
above the BIOS level (i.e., on the hard drive somewhere). Consider, if the
PC had no hard drive (or a dead one or a balnk one), it should still be
bootable from floppy or CD. Go back to the BIOS and try setting the boot
order. That may be separate from listing bootable devices, or it may be on
the same screen. If necessary, read the motherboard manual, or if a
pre-built PC, check their support website for more info, including possibly
a downloadable manual.
As for formatting a hard drive, if the drive (really the parition) is not
being used by XP, then XP itself would be the easiest way to format it. Use
XPs disk managment tool, or if the drive appears in explorer, just
right-click and choose format.
But, if you want to format the drive where XP is installed (usually C
,
then you must do that from outside of XP. Running the XP recovery console
from the XP CD is a possibility. Running the XP recovery console from a
stack of 6 or so floppies (free download from Microsoft) is a also a
possibility.
http://support.microsoft.com/kb/310994
However, the best bet might be to use the CD that came with the hard drive,
assuming that you installed it yourself. Or, download an ISO image and burn
it to CD from almost any hard drive maker. Such CDs also have disk testing
tools. Just avoid anything that sounds like "low level", since these tests
may be destroy pre-existing data everywhere on the hard drive. I have had
good luck with the Seagate tools:
http://www.seagate.com/support/seatools/
They also offer a a floppy version, but that does less, and its screen are
more DOS-like.