First, you should look for some built-in software that will let you create recovery disks, it's usually few DVDs.
Then use some software to backup that partition - check your drive manufacturer's website, they may provide some software for that. (for example WD has special free version of Acronis TrueImage for PCs with WD drives) Copy that backup to external drive or burn it onto a DVD.
Finally, insert Windows installation disk or previously prepared bootable pendrive and when the installer asks you to choose partition, select the one where Windows is currently installed. Installer should take care of the rest.
If you don't want to risk breaking something while installing new system, there are some programs that will help you remove bloatware preinstalled by laptop manufacturers - for example PC Decrapifier.