By default the password on most 3540 systems is null or blank. This applies to MCU's and Gateway web log in. As you reference the OS and VNC password I am guessing you are looking to access the AS module. If this is the case, here is some information I posted on another message.
====
Depending on the version of software you are running the defalut VNC password could be a couple of the following...
The default VNC password for certain 2.X or below should be "123" as displayed here...
http://www.cisco.com/univercd/cc/td/doc/product/ipvc/ipvc3540/as_mod/rel_1_0/appc.htm
For 2.2.x, 3.X and above it could be "admin"
http://www.cisco.com/univercd/cc/td/doc/product/ipvc/ipvc3540/as_mod/rel_1_0/rel_3/asrnv30.htm
The windows login should be user:cisco or Cisco password:admin by default. If it has been changed and you cannot get into the system, the IPVC TAC should be able to get get into the system with a support use only admin account.
---
Link to similar message post...
http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=IP%20Communications%20and%20Video&topic=Video%20over%20IP&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.1dd77ec6
