Hi Rami,
Welcome to PCHF.
The number of instances an application has open is determined by the application, not XP. It's normally up to the developer to provide such a facility. I've not heard of any external utility, but it would only take 5-10 minutes to create. I'll do this for you, and post it when I can upload it to a server.
EDIT:
Here you go:
http://www.mad-monkey.co.uk/resources/pchf/iutil.exe
- Save that into the same folder of the program you only want to run a single instance of.
- Right click on it, go to
Send To - Desktop (Create Shortcut).
- From the desktop, right click on the the real shortcut and go to
Properties, and press
[CTRL] + [C] to copy the contents of the "Target" field.
- Right click on the
iUtil shortcut and go to
Properties. Press the
[END] key to bring the cursor to the end of the "Target" field, followed by a space, and finally
[CTRL] + V
Do what you would like from here, maybe delete the old application shortcut and then rename and change the icon of iUtil.
If you would like me to explain the procedure more clearly, let me know.
Hope this is OK.
EDIT:
Marked as answered.