The updates on the Wikipedia entry on the 2008 South Ossetia War suggests, via Georgian news sources, that the Roki Tunnel (one of the key land routes into the valley that leads to Tskhinvali) has been destroyed. The Russians, obviously, deny this, but if it were to be severed, this would be deeply significant. The Wiki entries, based upon Russian news sources, are indicating that elements of at least one airborne division have been airlifted into Tskhinvali (likely by helicopter, as there is no airfield in Tskhinvali according to Google Earth), with another airborne division moving to follow. Light troops cannot holdout forever without armor, but it would suggest that upwards of three divisions (the 58th Army has one) are in the area or are in motion to the region.