1. Well, on most any other chipset, southbridge cooling is not needed at all. However, on the nForce2 chipset, it runs very hot. The MCP-T southbridge on the higher end NF2 boards has a integrated APU and Firewire, and tends to run a good deal hotter than SB's on most other chipsets. On the NF2 boards I have used, the SB is almost too hot to touch when running 200mhz FSB+.
2. The NB and SB heatsinks I used in this project are both attached with Artic Silver thermal adhesive. The NB HS used is actually a CPU HS unit, and using the holes in the board around the NB would have required drilling and modification. The SB on the Abit NF7-S has no holes around it, so the only way to attach is with an adhesive. On my 8RDA+, it had the holes around the SB too, so I used the regular push pins for that application.