iPhone supports the following authentication methods:

Pre-shared key IPsec authentication with user authentication via xauth.

Client and server certificates for IPsec authentication with optional user
authentication via xauth.

Hybrid authentication where the server provides a certificate and the client provides
a pre-shared key for IPsec authentication. User authentication is required via xauth.

User authentication is provided via xauth and includes the following authentication
methods:

User name with password
RSA SecurID
CryptoCard

IPSec (3rd option) is what i had to use.

Get the server name from the desktop vpn client... u gotta select the connection entry, right click, modify...new window pops up and u got all the details. select the server name from there.

Account name is your vpn username (most of the times will be same as ur domain username)

Password is ur vpn password...if using rsa key leave this blank

If u r using certificate i am not sure how to configure that...group authentication here...

Enter the group name exactly like the one in desktop vpn client

Group password is a little bit tricky...search for .pcf file in your system matching with the group name...open it with notepad or any of ur favourite text editor...it is a plain text file and look for "enc_GroupPwd"

it should be a long text...this is ur group password but it is encrypted...

copy this text and paste it in this website
cisco vpnclient password decoder

and click decode....u should get a nice decoded password next to clear:

that's ur group vpn password...type this in ur Secret option in iPhone

Save and connect....u will be asked for VPN password...insert the correct password and voila u r connected