How to block a contact in Gmail?

1. Click Contacts from the left side of Gmail.
2. Select the person you'd like to block.
3. Select Block from "Show in chat list" Box.

To unblock 
Just select Always or Auto from the "Show in chat list" Box.
OR
Type their name in the Search, add, or invite field at the top of your Chat list. Then, in the blue box that appears, hover over your contact's name and select Show in chat list.

Trick to chat with multiple accounts in GTalk

Create a Desk top short cut for GTalk

Right click on the GTalk short cut

Click properties

Select Shortcut Tab

In the target box change '/startmenu' as '-nomutex'

Click Apply and OK.

That's it! Now you can  use GTalk with multiple accounts.

How to save 'Chat history' in Google Talk?

OPTION -1

• Log in to GMail
• Click settings (in the top)
• Click Chat
• Select 'Save Chat History'

OPTION - 2

• Log in to GMail
• Click Chats (in the left panel below 'Inbox' and 'Starred')
• Click settings (in the right panel)
• Click Chat
• Select 'Save Chat History'

How to be 'invisible' when I am online in GMail? I don't want others to see me, when I log in.

Log in to GMail
Under Chat(in the left panel) select your name
Click the drop down list box against your name
Click invisible

That's it! You are invisible. You can see others, but others can't see you online.

Google Talk is recording all my chat details. How to stop this?

Log in to Google Talk
Select the name of the person (with whom you want to chat)
A separate chat box will be opened for you & your friend.
Click drop down list box (on the top left)
Click go off the record

This will prevent the 'Chat history' being stored (with this particular friend)

How to type bold text in Google Talk?

For Bold text in Google Talk
Start and end the text with *
Ex : *Hello*

For Italic text in Google Talk
Start and end the text with _
Ex : _Hello_

To increase or decrease font size in Google Talk
Hold ctrl key and use mouse scroll key.