make a box transparent

Hello,

Which parameters should I change to make a box (rectangle) transparent ?
For example like "highlight".

Thank.

-- 
---
==========================================================================
  Patrick DUPRÉ                      |   |
  Department of Chemistry            |   |  Phone: (44)-(0)-1904-434384
  The University of York             |   |  Fax:   (44)-(0)-1904-432516
  Heslington                         |   |
  York YO10 5DD  United Kingdom      |   |  email: patrick.dupre@...
==========================================================================

------------------------------------------------------------------------------
Benefiting from Server Virtualization: Beyond Initial Workload 
Consolidation -- Increasing the use of server virtualization is a top
priority.Virtualization can reduce costs, simplify management, and improve 
application availability and disaster protection. Learn more about boosting 
the value of server virtualization. http://p.sf.net/sfu/vmware-sfdev2dev

------------------------------------------------------------------------------
Benefiting from Server Virtualization: Beyond Initial Workload 
Consolidation -- Increasing the use of server virtualization is a top
priority.Virtualization can reduce costs, simplify management, and improve 
application availability and disaster protection. Learn more about boosting 
the value of server virtualization. http://p.sf.net/sfu/vmware-sfdev2dev