It is possible to search for the user in AD given only their username and
you can get all of this information (although groups can be tricky).

However, you need a security context that has rights to access AD.  If you
want to access AD using the user's own security context, you either need
their plain text credentials or a Windows security token that you can use to
impersonate them and access AD.  If you want to use a different account to
access AD, then any valid service account that has the rights you need will
do.

So, it depends on what your model for accessing AD is.

There are lots of code samples in the System.DirectoryServices SDK topic in
MSDN.

Joe K.