[mudsliptones]

okay, a format is hard the first time you do it
believe me, I had this old comp and well, I formatted and wonder by wonder, the CD rom install disk didn't worked!!!!!
so I was without a discdrive, so no windows aor anything, had to ride my back allot of miles to get a working one

but okay, look, first I need to know what os you have
linux, windows, wich versions

if you do a format remember you'll loose everything that you haven't put on a disk!!!!!!!
another option is, if you don't have a cd writer, partition your harddisk in 2 disks with partitionmagic (best proggie to do it)
just drag every file you wish to keep to the 2nd disk, and format the first
later you can drag the files back to the formatted disk

okay, to format, you definetly need a booting disk of some wort (windows has it)
if you have a newer comp you will have a cd rom available after formatting (I didn't had it years ago)
in dos you just type the format c:/ command and click yes blabla
all your shit is gone...
now
this is what you need to do if you have a wiondows version liower then xp:
reboot the comp and go to the bios (mostly hit de delete button)
then search for a boot sequence, just set the first boot from a: (so your disk drive)
restart the comp with the boot disk inserted, you get a menu, choose boot comp with CD rom
bam, your in dios, BUT you have a CD rom player available
insert the windows disk and go to it via dos
mostly D:
so you just type d: *enter*
setup *enter*
bam, windows will install

with XP it's different, it's far better although I haven't figured out a good way to install it, the disk cann,ot run from dos, so you format and then again got to the bios system, choose now the cd rom as first boot device
windows XP will launch after you restart (with the disk inserted)
at one point your comp will restart automaticly, be sure to change the first boot device to your harddrive otherwise the windows XP will launch again and you'll be working in a circle
the setpu continues

after windows i installed you'll need to configure the comp---> videocard, soundcard, nerwork adapter, internet
this depends on what you have, mostly windows XP will recognize everything and install it together with the setup