Freeze mouse pointer and let scrollwheel work

I have a wireless mouse in Vista. I need on demand to lock the mouse pointer when the mouse moves but have the scroll wheel scroll vertically as normal. Meaning lock the pointer only, not the whole mouse. Scrollwheel should work at all times. There should be a hotkey to lock/unlock the mouse pointer in place. The pointer should be locked at the position where the hotkey was pressed. This functionality needs to work in Adobe Acrobat. The hotkey is shift + left mousekey. One press locks the pointer, another press unlocks it. App preferably written in C# and has an icon in the system tray.