"Can I install Windows 8 on my laptop?"に関する回答You will need to make sure that your system matches the system requirements for any OS you’re planning to install. For Windows 8 and 8.1 follow this link here to check the system requirements. If you’re interested in installing any other OS, follow this wikihow guide to see a more detailed description of how to install a new OS.
"Can I use a different watt power adapter?"に関する回答Yes, both power adapters should work fine for the Thinkpad. However, there may be limitations for the 65W power adapter: the battery will take longer to recharge and it might not be powerful enough for certain types of usage (ex. watching a DVD while at the same time running HDD intensive applications).