Ubuntu and WinXP

[squareyes]

Hi all,
yesterday I  formatted a missbehaving win XP drive for a neighbour,
and finally managed to get him to allow me to install Hoary. Both Win XP 
and Hoary were working
fine when I left.
He does not have Internet connection so I was intending to use
Unofficial 5.04 Add-ons cd for the extras he needed. gave him a CD I 
made up with help on it.
This afternoon I called in to see how he was going and was told he had 
un-installed Hoary,
as it caused WinXP to keep on crashing, which was cured by the un-install.
As I had to format the drive for him in the first place (he had 2 copies 
of XP on it)I don't see how he could have removed it
and reclaimed the partition I arranged for Ubuntu,( partitioned with 
Partition Magic) but thats a separate story, my question is
Is it possible for Ubuntu to interfere with WinXP or visa versa when 
it's on a separate partition?
I can't see how it could, partitions were 2 X 20 gig  Any ideas would be 
greatfully received.
Could he have a hardware problem?
Thanks in advance.
Take Care
Winton