Under the terms of the agreement, customers using Intuit's small business and personal finance products will be able to use PayPal as their default payment method. In addition, Intuit's software products will be available on X.com's Web site, the company said in a statement.
Additional terms of the agreement and details of how X.com's Internet-based payment services will be incorporated into Intuit's products were not disclosed.
Intuit, based in Mountain View, Calif., builds accounting and personal finance software for small businesses and consumers such as Quicken and TurboTax.
PayPal, a service that allows customers to send money via email, is free of charge to individuals, but charges a 1.9 percent and 25 cent transaction fee for business use.
Since its November launch, PayPal has become one of the most popular online payment methods, according to analysts. In less than a year, Palo Alto, Calif.-based X.com says it has 3.6 million customers using the service, with 200,000 of those being business customers.