To migrate your Contacts information, you have to do it
through the Export/Import function in Contacts.
Thus, you Export the details into a .csv file (created on your PC)
from the source account. You then need to log out of that
first account, log in to the other account, and then Import that
same .csv file into the new/second account.
Reading the many sections of
http://mail.google.com/support/bin/topic.py?hl=en&topic=12867
- from Gmail's Help pages, will give you all the Help you
need to understand the process.
As far as moving all the messages, this is a much more complex issue,
and can probably best be done through using IMAP and an e-mail client
such as Outlook.
It involves setting up Lookout to use IMAP into your first Gmail
account, transferring that info to your local PC, disconnecting that,
then setting up Lookout to use IMAP to your second account, and
sending the information back to that new Gmail account.
The easier alternative is to perhaps use Gmail Backup (which is NOT a
Google sourced program!) or Gmail Keeper to download a backup of all
the messages in your original account, then connecting Gmail Backup/
Gmai Keeper to your new account and restoring all the data back into
that new account.
I personally would advise everyone to have a backup copy of their
mailbox data, in case their account gets compromised. And Gmail Backup/
Gmail Keeper seems to work so straightforwardly, allowing you to store
to a (temporary) USB-connected disk.
Note: this is NOT a 'working copy' of your mailbox data - it is a
genuine Backup which would need to be restored to make it usable. NOT
to be confused with Offline Gmail!!