if it is text files that you want to save or transfer to a new computer do like i do and email the documents to yourself, that way there is always a electronic copy that you can access anyware, create a file in your inbox for the documents so that they are not deleted by mistake, encript them if you are worried that they might be read,

the best way to erase all the data is to format the hard drive, to do so just insert the operating system software, (your xp disc) and choose install fresh copy option, do not use the quick format option, do the full format option to make sure everything has been cleaned.

oh and before you do erase all your data make sure you have the passwords to your email accounts, web sites that require you to sign in ect