Yes Nani even if u opend google the browser,if run another 
script,script will open another web page   and performs 
wat ever u wrote in that script.

For example i am providing a script for opening a 
google.co.in web page and seraching for 'search' on goolge.
Code:

Set IE = CreateObject("InternetExplorer.Application")
IE.Navigate "http://www.google.co.in"
IE.Visible = True
Wscript.Sleep 8000
IE.Document.All.Item("q").Value = "serach"
IE.Document.All.Item("f").submit()

Copy above code in notepad abd save it serach.vbs on desk 
top.

then click on file after saving it desk top.

this scripts runs and opens goog.co.in web page.
if u click once again it will open again a web page.

If u have any doubt please mail me

byee
Rajendra Prasad Reddy
rajendra_penumalli@yahoo.com
Test engineer
Hyderabad

I Guess this depends on how u have recorded the script.
Case1:
 if u have recorded the script with many google
pages(windows) open, as there are many windows open, QTP
identifies the ordinal identifier and stores it in the
repository.
So if we run the script, in this case you will not encounter
any problem even if there are hundreds of such windows.

Case2:
 If u have recorded the script with only one google window,
QTP will not store the Ordinal Identifier as it can clearly
identify the window we have specified.
So if we run the script, after opening many google windows,
QTP cannot identify the window in which it has to perform
the operations. so it returns an error.