You can re-use your code for different installations (not sure if that applies under EULA - End User License Aggreement), but it works. I have EQ installed on multiple computers, but of course only a single account, so only one computer can be logged in at a time. :(
You should read the EULA though to make sure it is legal, as I haven't read it since I first installed it 3-4 years ago. I have multiple editions of EQ, and know that I have re-used the original number. But because of the multiple editions I have, and even used to have multiple accounts from different CDs, I am sure that is legal (except for possibly re-using the number).
I even recently re-installed my original copy to run the original tutorial off-line to see how much different the UI (User Interface) is. It is so much better now :P
[From EULA file license.txt]
7. Subject to the terms of this Agreement, we hereby grant to you a non-exclusive, non-transferable, revocable license to use the Software solely in connection with playing the Game via an authorized and fully-paid Account. You may not copy (except to make one necessary back-up copy), distribute, sell, auction, rent, lease, loan, modify or create derivative works, adapt, translate, perform, display, sublicense or transfer all or any portion of the Software. You may not copy any of the written materials accompanying the Software. You may not reverse engineer, disassemble or decompile the Software except to the extent that this restriction is expressly prohibited by applicable law. The Software may contain license management software that restricts your use of the Software.
I take this to mean, that multiple installations for your own computers is ok, but that could possibly be construed as copying, as I am not lawyer, and it is not as clear as some definitely more restrictive licenses I have read. I think it is some of the Adobe license, that specifically state that a license must be purchased for every installation on every computer, and for each person that may conceivably use that computer. So that, installing there software on a public computer, would require licenses for every potential user of it.
Edited, Fri Jan 2 00:29:28 2004 by Yther