Turns out I made a very early and very crucial mistake. I did an early search to find the suggestion that the key for the AV is located at ldlogon\antivirus8\av.key. I imported this key, and everything seemed to be hunky dory. In reality, the key is valid, but not for licensing and activating AV. Instead, I found How To: Troubleshoot LANDESK Antivirus, which suggested that I would need to contact support, and they would email the key in a .zip file.
On a whim, I checked back in the original email, which contained the username and password, and sure enough, there was a .zip attached that I overlooked, as it didn't say anything about it, nor the importance of it. Inside was the key that I needed to license LANDesk Antivirus.
Seems like a rookie mistake, and I'm a rookie.