I used remote assistance with windows XP yesterday.  Ever since the
session ended my keyboard is misstyping.  Meaning the letters I type
are not the ones that appear.  The keyboard seems to be mixed up. 
What could cause this and what can i do to fix it?

unplug and replug your keyboard in, start from the basics, no sense in
restoring your computer if its with the cabling

Is there any way you activated some settings for, say, a Dvorak
keyboard, or a different language keyboard? I don't know how to do it,
or undo it, but maybe someone else does.

I found a couple of really interesting sites that might help you.
(You've probably already got it sorted, haven't you?) But just in
case, have a look at these...

I read a site that said that with Remote Assistance, it seems that
whoever is helping you can change your keyboard settings very easily.
I bet that's what's happened. Read about it here:
http://www.telegraph.co.uk/connected/main.jhtml?xml=/connected/2005/01/12/ecrboot12.xml

In particular, from that site, there's this:

"One final point to watch out for, whilst you are controlling a remote
PC you will using the other user?s mouse and keyboard settings, which
means you may accidentally encounter unfamiliar keyboard shortcuts, or
reversed mouse buttons, if they are left-handed."


And this site has a good tutorial about how to set your own keyboard settings. 
http://tlt.its.psu.edu/suggestions/international/keyboards/winkey.html

Hope this helps. Let us know how it ends up, won't you? It's a really
intriguing problem.

Well I performed a system restore and everything is back to normal.  I
think stressedmum-ga had tha answer.  When you use remote assistance
the control PC's keyboard and mouse settings are changed on the remote
PC.  Thanks for all the efforts on this issue.