How to import .PRX file to P6

try checking this

http://www.planningplanet.com/forum/forum_post.asp?fid=1&Cat=8&Top=47213

Salman,

In addition from extracting PRX file and converted to P3 file and you are using 64-bit, in order to use the P3 import/export functionality in P6, you must have P3 installed on the same machine where P6 resides. Additionally, you must complete the steps below to register a required DLL file.
1 Open a command prompt.
2 Change your directory to the location of the “ra32.dll” file. By default, the path is C:\Program Files\Common Files\Primavera Common\Ra.
3 Execute the following command: regsvr32 ra32.dll
If you do not want to install P3 on the same machine where P6 is installed or are using a 64-bit operating system, you can instead have your P3 users use a separate P3/XER import/ export utility available from the P6 common files (by default, the location is \Program Files\Common Files\Primavera Common\Convert. Refer to the Oracle Primavera Support Knowledgebase for more information