Intellimouse Bluetooth Problem on Snow Leopard

I have a clean Snow Leopard install on a 24" C2D iMac, and its all working perfectly with a half-knackered mighty-mouse.

So, I purchased a Microsoft Bluetooth Notebook Mouse 5000 and set it up today.

I'm finding that if I leave the Mac, after ten minutes or so the screen goes to power save but not sleep, and after around 20 minutes total the screen kicks back in to tell me the mouse is no longer connected.

Touch the mouse and it comes back.

If I put the Mac to sleep manually I only have to touch/move the mouse and the Mac wakes vs. actually clicking or doing something deliberate.

I'm assuming the mouse is going to sleep/power save to preserve the batteries, but I'd expected either it, or OS X, to deal with this a bit more gracefully?

I installed Intellipoint, no difference.

Appreciate any pointers if it's OS X, the mouse or if I'm just asking too much expecting a 3rd party mouse to behave the same as an Apple one.

Thanks in advance.

 

Blimey.. anyone? Can't be the only person using this combo surely?