I've had no problems with my user accounts on my desktop but I did have a problem on my recently aquired laptop. I'm not sure whether these problems were as a result of downloading the dialler or whether the problem was 'embedded' in XP from the beginning.
The problem I had was that windows was not remembering my passwords. See topic:L
Windows passwords forgotten
Richard from Naples Air Centre pointed me to this link which did the trick:
Bill G knows about this problem and has a fix
Regards
Exeng