Sleep Mode - disconnected, automatically reconnected after sleep m

I have the following problem -
I like to manually connect and disconnect from the internet... I've heard
that it is the safest way to protect myself from unauthorized access, but
anyway, this is what happens:
- I manually connect, and disconnect when I want to work only on my hard
drive.
- I may decide to walk away for some time, and put my laptop in sleep mode
- when I come back and recover from sleep mode, my wireless network
connection to the internet is restored.
- I would like to change the setting somehow so that again, if I want to
reconnect to the internet I do so at my will.
Using Vista Home Edition Premium - Any one have any thoughts on this?? Thanks!