It depends on your PC if the lag is removable or not. If you had given the PC specs I could be more clear.
Windows 7 needs a multi-core processor and 1GB RAM of it's OWN to work seamlessly so make sure you do. Also, more RAM means more efficiency. So get extra RAM, you need atleast 2GB+ to run Windows 7 fast.
Another thing could be the start-up. Uninstall the programs you don't need (Control Panel - Programs and Features - Uninstall ) and remove the programs which are not to be started when you start Windows.
- Run (Control + R keys) ( or on the start menu)
- type 'msconfig.exe' without quotes
- select Boot tab
- click hide windows services
- uncheck the programs you want to disable on start-up
You have much free disk space so don't bother about it. Also, Minecraft is not a much optimised game! So don't expect to run it so great without a graphics card. If your PC is more outdated than 2008, I suggest for a new upgrade for the PC.
Feel free to contact me if you need help :)