On day 31 I think you will be stuck. You will get a message "You must activate Windows before you can log in"
Simply connect the pc to the internet, activate windows, and disconnect from internet.
You can still get updates fro XP but be aware you will need to download and install Internet Explorer 8, before XP will connect to Microsoft servers.
If you want to keep this PC connected, use Firefox as default browser, keep antivirus up to date and it will be fine.