Find IP address by AD username?

Using a LDAP browser tool like Softerra, I believe you could find the machine name being used by the username by querying the domain controller...then you could ping the machine name to give you the IP address.

I don't believe that you can directly enumerate username remotely, but I could be wrong.

With psloggedon, you can see who is logged on, but you would still need to ping the machine name to get the IP
http://technet.microsoft.com/en-us/sysinternals/bb897545.aspx

So the long way around the barn would be to:

1) Enumerate machine names in AD:
http://www.myitforum.com/articles/32/view.asp?id=9449

2) Enumerate logged on users, using psloggedon,

3) Ping enumerated machines, to give IP.

4) Correlate logged on users to IP addresses, based on step 2 above.

I created a "Lookup User (LUSER)" script to do just this. It works by querying network session information on remote servers (file server etc). It will need tweaking for your environment but hope it helps :

http://www.safetoland.com/pctools.html