As I'm sure you are aware, there are a number of HSF's available for 775 motherboards.
Freezer Pro's are cheap and highly effective. They use the same fitting system as the intel stock cooler. The only things i'd say is that you should *always* remove the motherboard to fit the HSF. If you do that, and clipping opposite corners on turn, then only minimal pressure should be required to clip the HSF into position.