Install Google talk, right click the Google talk desktop icon->Properties->Short Cut tab->Target->Append at the end with the following string with out any quotation.
” /startmenu /nomutex”
Note: there is a space before first forward slash as well as second forward slash.
Click Ok button
Now double click on the google Talk icon as many times as u want and login with your different Google id’s.
Happy Chatting 🙂