AM buying an 06 325i with 77k miles. Am told this model is prone to needing radiator and hoses replaced at around 100k. am told just do it now to prevent problems. What will it cost?

So, this should be the least of your concerns. Under $500. There are many other things that can go wrong costing much more.

Is it running hot, why do this now?.

Or, maybe you just need new hoses? I wouldn't replace a working radiator unless you just want to spend the money.

Really...Mark is right. If it ain't broke don't fix it!

For the 325i, the problem is not the radiator but the coolant expansion tank. Also, water pump and thermostat shoul be replaced before the 100k miles. Why? Because on bmw, overheating for 2 seconds is equal to headgasket issues. Cost of replacing water pump, thermostat, hoses and expansion tank:$1200.00 Honestly, that's worth the investment, that's an excellent car but needs to be maintained in order to fullly enjoy it.

Thanks everyone. Haven't got the car yet and am having mechanic look at it on Monday. Do not want the car to ever overheat as have read nightmare stories about that; need the car to be reliable so would rather address known issues in advance or at least be on the lookout. Would the car run hot for a while if cooling system is failing or does it happen suddenly?