Perl4 to Perl5.6.1 up gradation.

[Mani.Kandan]

Hi,
 
Currently we have Perl4 installed in our Environment, We are planning to
upgrade to Active state Perl 5.6.1.(626).
 
 
1. what are the precautionary measure we have to take before upgrade?
2. Whether the Perl4 programs work in Perl5.6.1?.
3. How will we set the environment variables?
4. Is this version is binary compatible?
 
Commands related to  up-gradation and difference between Perl4 and Perl5.6.1
are welcome.
 
Thanks.