They are a large hardware vendor. I wouldn't consider them a competitor to Epic or Cerner. In fact, HP and Cerner are partners.

Cerner is a leading provider of clinical and management information and knowledge systems for organizations in the healthcare industry such as hospitals, medical centers, and patient care facilities. Cerner's unified health management applications, equipment services, and technologies give healthcare institutions comprehensive, enterprisewide information-processing solutions that handle equipment tracking, materials management, records management, and financial accounting for improved quality of care, shortened hospital stays, and reduced costs.

A member of the HP Developer and Solution Partner Program (DSPP), Cerner has partnered with Hewlett-Packard Company for more than 15 years. This close technological relationship helps Cerner solutions leverage the scalability and load-balancing features of HP OpenVMS systems on HP AlphaServer platforms to create high-availability environments that support the needs of 24 x 7 healthcare organizations.

http://h71000.www7.hp.com/partners/c...

Also from their site:

Start your EMR implementation with an evaluation of existing EMR software packages. This is not the kind of system you want to spend time creating from scratch; many vendors sell excellent off-the-shelf or customizable EMR systems that help you input, manage, and distribute records in standardized templates.

http://www.hp.com/sbso/solutions/hea...

As a enterprise hardware supplier, HP is a leader, sure. In my experience, I'd say Dell is bigger in the health care space but don't quote me on that one.