If you work in the same department, are in a supervisory situation, or if your jobs require quite abit of collaboration even if you are in different departments, then don't do it!
IF where you work is relatively large and you hardly ever interact with each other, then it should be okay. Most larger organizations will probably have a written policy about this and it shouldn't be so hard to find. Most likely, it will be part of your company's sexual harassment policy.
find out the policy, if you can have a relationship, then proceed with caution.
this is our policy. i work at a university, so student/professor relationships are also covered:
"It is essential that those in a position of authority not abuse, nor appear to abuse, the power with which they are entrusted. Administrators (including all staff who supervise other staff or students) and faculty members exercise power over subordinates and students. Therefore, amorous, dating, or sexual relationships between administrators or faculty members and subordinates or students are highly discouraged when these administrators or faculty members have professional responsibility over the subordinate or student. Relations of a sexual nature that may appear to be consensual are still suspect, given the fundamentally unequal nature of the relationship. Moreover, other employees or students may be affected by the relationship, because the administrator is in a position to favor or advance one person’s interest to the potential detriment of others. Therefore, it is
inappropriate for administrators or faculty members to engage in an amorous, dating, or sexual relationship with a subordinate or student where the administrator, or faculty member, will be required to make professional judgments about the subordinate’s or student’s work or academic performance. The University requires that the supervisory employee cease such conduct and/or divest himself or herself of the professional responsibility for supervision or oversight, should an intimate relationship develop."