Although I had suggested getting the serial number of users' drives, I never suggested actually scanning the drive. You can get hardware serials through WMI (for an example, go into command prompt and input "wmic bios get serialnumber"); the only really "tricky" part about it is verifying that the hash goes unmodified by external applications, which can be remedied by encrypting and signing the hash, then verifying the encrypted hash against a central server (which also does the signing). The issue then becomes preventing malicious users from just sending false serials to the central server and generating new, valid hashes. Though not perfect, you could require these hashes to be tied to user accounts (send forum login info on hash calculation). People would be far more skeptical of hack applications when they also ask for user login information, and might choose to avoid it all-together. This would also allow you to ban all of their systems in a single swoop, as well as limit the number of systems for a given user in a given month (very few people would play Renegade X on 10 different systems during the same month). Ban systems could then be adjusted accordingly to forbid IP addresses, hardware hashes, and forum accounts with the use of a single command, which at a minimum would severely complicate the ban-evasion process.
While that idea is still far from perfect, it would certainly demolish most people's attempts to ban-evade by changing their IP address.
Edit:
As for a global ban system, there is some need for consistency for repeat-offenders. If you're banned on 2/3 of the servers for cheating, you might as well go ahead and just get globally banned. That said, there should be very few bans added to such as list; if there's more than 1 or 2 every other week, there might be a problem.