dmi pool error sounds more like the operating system is corrupted than a virus. reinstall her operating system after you saved all her files to floppy disks or on another storage media.
you can hook her hard disk up to your computer to copy the files if they are too large. saving data is very important so make sure you don't miss anything important.
after saving data you need to reinstall the operating system. installing an operating system is different depending on which one it is. the most common are windows 98/ME/ 2000/XP.
doing it this way from scratch requires that you have all your device drivers and software ready before you begin.
before you try that please understand that many computer manufacturers have restore cd's. this makes it more simple, all you have to do is put the restore CD in the cd-rom drive and restart the machine. you than follow the directions given.
this method is easier than doing it from scratch which requires more knowledge, learning. I've only given you general help, you will propably need to ask more questions and give us more details of the computer you will be fixing.
please list the operating system it had, and the make / model of it.
as for checking for boot sector virus here's alink to the norton anti-virus software. you can download a free trial version and use it for a limited period of time. click "try now!" to download it: