I have an old computer which runs Windows 98, Second Edition. So, could anyone tell me how to enter the BIOS so that i can alter the boot-sequence so that the computer will boot-up from the CD drive please.
Have a look at this page - scroll down to the third screen (Advanced BIOS features) and you can click the screen to enlarge it. Where it says First Boot Device, Second Boot Device and Third Boot Device you move the cursor to "First" with the Up/Down Arrows and then change the boot option to CD using the Page Up/Page Down keys. Then, as Totally-braindead says you must save it before exiting.
The exact layout may be different depending on your motherboard, but will operate the same way.