I see that current prices on the A64 3000 90nm for the Retail Box at several sites is either the same or slightly cheaper thatn the OEM version. Would it make sense to buy the BOX just because (free heatsink and fan).
Of course. The OEM only has a 1-year warranty (and no "AMD-certified" HSF) while the Retail CPU comes with a 3-year warranty and the AMD-supplied (and obviously approved/certified) HSF.
Of course planning on Overclocking.
Other than the afore-mentioned 3-year warranty and HSF, the Retail CPUs' are supposedly no different than the OEM CPUs. (Years ago I had a suspicion that "marginal" CPUs were packaged as OEMs, with CPUs' displaying better stability packaged as Retail. That way, if a CPU died within the OEM's 1-year warranty the CPU manufacturer had no obligation to warranty the CPU). That theory really doesn't hold water, as Intel and AMD sell millions of OEM CPUs' to large and small system integrators worldwide (and they wouldn't shoot themselves in the foot by selling "weak" CPUs' to vendors, would they?).
So as far as overclocking goes and all things such as cooling systems being equal, the Retail (boxed) CPUs hold NO advantage OVER OEM CPUs'.