The promotion is retroactive to May 1 and runs through June 30, according to the company.
Big Blue joins Gateway and Dell in making free upgrades available to new PC customers. The upgrade's retail price will be $109 for users with previous versions of Windows installed, and $209 for users with DOS or no operating system at all.
All of the upgrade promotions are part of an effort by PC makers to address customers' reluctance to purchase systems before the widespread availability of Windows 98. But it's unclear how government action to delay the software's release would affect the promotional efforts.
Reuters contributed to this story.