The actual limits are dependant on the version of your database. You can get the information in the Oracle Reference manual (not the SQL or PL/SQL or Netowkring or ... Reference, just 'Reference') in the Appendix entitled Database Limits.
For 10gR2, the manual can be found here
pransuj, if you are unsure after looking at the referenced document you can have as many columns in your PK constraint as you can define in an index definition, that is, 32. This is subject to the key length limitation specified elsewhere in the documentation.
HTH -- Mark D Powell --