If you want to run two or multiple instance of Google talk Gtalk IM messenger signing-in with different google accounts, just follow this trick.

Create or edit the existing shortcut of google talk appending with /nomutex at the end.

A typical google talk shortcut will look like "C:\Program Files\Google\Google Talk\googletalk.exe"

You just need create one more shortcut or edit which looks like this: "D:\Program Files\Google\Google Talk\googletalk.exe" /nomutex