Do you want that your multiple gmail id's can login from a single machine simultaneously, then just follow this steps to get the multiple instances of gtalk.
1) create a shortcut of gtalk.exe on desktop.
2) right click the shortcut link, and goto properties.
3) In target text_box type "c:/program files/google/google talk.exe" /nomutex
4) click ok and refresh the desktop.
Now you can create multiple instances of gtalk and access your all gmail accounts simultaneously
.Copy from one, it's plagiarism; copy from many, it's research