Ubuntu installation for technophobe

I've been asked to remove the malware or "scareware" Antivirus Action from an old laptop (IBM Thinkpad?) with a square screen and CD-ROM drive, as well as to install Ubuntu Linux. I don't know the size of the hard drive. The laptop's owner is a bit technophobic, the laptop was bought second hand, may be 10 years old, the hinge supporting the screen has recently broken and the cursor down key is falling/has fallen off. It has some USB ports. I don't know if I can persuade the laptop owner to have the keyboard repaired, replaced, or to use a plug in USB keyboard. I've already given him a quick tour of Ubuntu Linux, which he seemed to like. The problem is the broken cursor down key and GRUB. My version of GRUB lists Linux as the first four or more options, then Windows XP further down the list. To select any of them except the first Linux option on top of the list, I need to use the cursor down key, which is broken on his laptop. How can I get round this problem? Can I somehow reconfigure the keyboard to accept another key as cursor down? Can I rearrange the order of these options? Of course he can easily buy a plug in USB keyboard, but he has to agree to this. Any ideas, please.