public-key encrypt and decrypt a string using a digital certificate.

Hi,
I need to encrpt a message using a public key from a digital certificate and 
Things that I have been able to do so far.
Read certificate Read public key from cert Now my message is a simple string message. I want to encrypt it using the public key and later on decrypt it.
(Also there is one big confusion in my mind, as to wether i can encrypt with public key and decrypt with private key ?? )
 
Also while googling on this, i found many types of encrptions like HASH, PCKS, DES, RSA i frankly dont know what they mean.. which one is suited for my need.
Please help. 
Thanking in advance,
Yasser R Shaikh.
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