I have old pc with W XP.
It runs very slowly and needs purging but I am nervous of decompatablising some of the XP functions.
If i load Linux first will I avoid that risk? R

I am not sure what you mean by "purging". There is a freeware program called CCleaner that will clean it up. http://www.filehippo.com/download_ccleaner/

There are different ways to use Linux without messing up Windows. Have a look at http://www.everydaylinuxuser.com/2012_09_01_archive.html

How Linux will perform will depend on how much RAM (memory) you have. There are some lightweight distros where you have little RAM.

If you LET Linux it will completely overwrite and remove all traces of XP...

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