Microsoft has begun disclosing how it will let Windows XP users replace its software with rival programs.
It's planning an upgrade that will make it easier for consumers to use other firms' email, web browser and instant-messaging tools.
Microsoft says it will offer the changes in a 40 megabyte service pack, probably in August.
The US government demanded the action as part of the landmark anti-trust settlement signed last year.
Nine state attorneys general are still pursuing tougher penalties.