I use LogMeIn which lets me long into a client's computer and do stuff from the internet. It didn't happen yet but I guess that eventually some users could be reluctant to this approach.

Is there a tool (XP and VISTA needed) that would let users know who did what on their computer.

I need a tool that would let the user check what I did on his computer. Having such a tool would make it easier to convince reluctant usera.

For example with that tool the user would be able to see that I only went on his computer and only used/updated things related to our apps and nothing else.

It would be additionnal security for them.