How to use remote microphone on Remote Desktop

Have a look at this page on VLC remote

Their program let's you control VLC over a network.

In regular VLC you can go to the File menu, choose Open Capture Device. Under the Direct Show tab, select the Audio Device Name from the drop down menu. Your device should show up in this menu. If not, check your microphone connection or click the Refresh List button.

Also check out this Engadget article on streaming with VLC, there's even a web-interface

By default accounts without passwords are restricted from logging in via remote desktop (they are limited to console logins only). You can override this by following the steps below:

To configure the Remote Desktop host computer to accept user name with blank password, go to Control Panel -> Administrative Tools (Under System and Maintenance in Windows Vista) -> Local Security Policy. Alternatively, run GPEdit.msc (Group Policy Editor).

Then, expand Security Policies -> Local Securities -> Security Options (for user using Group Policy Editor or GPEdit.msc, expand Local Computer Policy -> Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options). Locate Accounts: Limit local account use of blank passwords to console logon only policy, and set its value to Disabled.