I'm assuming you mean Icetcp Pro in all these questions (Iceten is a different product).
First question:
When running on the new PC, open a explore window and browse your network to the computer that has the Pro licenses on it. You should be able to browse to the folder called icetcp5_user on that computer. That folder might be visible directly over your network or it might be under the ICETCP5 Server folder (which my be under the Program Files folder). In the Icetcp5_User folder there should be an executable called setup.exe. This will start the client installation. At the end, the ConfigWizard should run automatically, and find the proper license folder for getting a sequence number.
Second question:
You can install the User (client) portion of Pro directly from the CD, but then you have to run ConfigWizard, and then browse (over the network) to the license folder on the admin computer in the dialog box for obtaining a sequence number. The preferred way is to do the user install as described above.
NOTE: The Admin portion of Pro should ONLY be installed on one computer in the network. Otherwise you run the risk of getting duplicate sequence number errors (as in question 3).
Third question:
Go to the computer with the licenses (the admin computer) and run the licenseadmin program (should be able to get there through the Start button). Go to the users tab and manually delete the entries for the 2 users with the sequence conflicts. Run the ConfigWizard on each the two computers, which then will get (re)assigned unique numbers (make sure both computers are going to the same license folder, on the ONE admin computer).