How do you get an application to take control of an audio device in Win Xp?

I'm trying to hook my guitar to my computer using my sound card. I've fixed any latency issues with ASIO4all drivers (that's fine). My problem is that when I start windows I can already hear the guitar playing without using any additional software (guitar rig 2 is what I'm using). So when I use any kind of software or VST plugins I get the original sound of the guitar (clean sound) along with the effects i'm trying to use. I was wondering if there was a way to get the software to take control of the guitars sound (or line in input of the sound card) in win xp or do they only have that option in vista. It's frustrating because i've searched all over the internet and I know that other people have the same sound card drivers as i have(ac97) and it has worked for them. Any help would be appreciated.How do you get an application to take control of an audio device in Win Xp?
You might try updating your drivers.