I recently booked a Business Objects Data Integrator exam (DMDI201) at the Pearson Vue website.
On this occasion I noticed that the Pearson Vue website now requests that you enter your SAP User ID:
Submitting my SAP User ID allowed me to continue with booking my exam.
If you don’t have a SAP User ID, how can you book an exam? In the first instance, I suggest you contact your regional SAP Support office. They should be able to set up a SAP User ID for you.
This post on the Business Objects forum suggests that people are able to get their SAP User ID’s by contacting support.
Give them a try.