1: NT boots up in stages. The GUI starts up before many of the services have finished starting up. The services database is locked until all services have started (or failed starting, and finished trying) It may be as simple as waiting a few minutes after login.
2: Are you logged in as administrator? If not, that is definetly the problem. You need administrative rights to add hardware drivers.
3: If you are logged in as administratior, then it's possible that the previous owner removed some of it's rights. Use regedt32 to explicitly give administrator full rights to the registry, and use explorer to grant full rights to the C: drive. (recurse the changes down through the hive and subdirectories)
4: I would strongly recommend a reinstall on general principal. Who knows what problems you're inheriting? [sig][/sig]