Nothing beats decrapifying a new computer as wiping its HDD out of the box, installing Windows, drivers and the software YOU plan using. This generally will make a very noticeable improvement in performance over just trying to uninstall the unwanted crap from the factory installation.

Unfortunately, most manufacturers no longer offer software installation discs with the PC, let alone the Windows OS disc. While most do give a "Create backup DVD" option, this usually only creates a DVD set that restores the computer back to its factory state, i.e. along with all the crapware. So most users are out of luck unless they know someone who can lend them a Windows 7 installation disc.

Some business PC/laptop models (i.e. with Windows 7 Professional) still come with installation discs and tend to have less pre-installed software than consumer PCs, so it may be worth a little extra for a business model.