Hi there:

I have been working in PeopleSoft as Customer Support Analyst for the past 3 years and I will be taking a new role as "Peoplesoft Security Administrator"

What is the best book that I should buy?

Any suggestion by existing Security Admins welcome.

I would suggest your first source of knowledge on PeopleSoft Security should be People Books. Go through the Security Administration part.

Also I suggest some Red papers which are available in Customer Connect, you need to have CSC ID to login:

LDAP Security with People Tools:
http://www.peoplesoft.com/media/cupa/pdf/red_paper/rp_e_tools_ldap.pdf

Securing your PeopleSoft Application Environment. Even though it is 3 years old and might have been written for older version of Tools, the concepts are almost same:
http://www.peoplesoft.com/media/cupa/pdf/red_paper/secure_environment.pdf


Another online public presentation on Security by Deloitte, which might be useful:
http://www.auditnet.org/docs/erppeoplesoftsecurity.pdf

If you feel after going through all these, you can find some books, but most of them repeat what you have in the above.