have you tried using apt-get? i could maybe provide some more insight if its really a connective issue or not...

and there are some idle time setting, just tap the wifi icon in the statusbar/tray and hit settings on the menu, then on the right side tab there are timeout settings for bluetooth and wifi. still, i have a feeling thats not whats going on here as that should result in the whole tether connection going down (bluetooth icon going white and all that).