Ok, you shouldn't consider a HD cooler unless you are uncomfortable with how hot the HD is getting during actual use. (to the touch)
The reason the lady asked you what hard drive cooler you were gonna use is..... She was trying to sell a hard drive cooler.
Either that or she is under the mistaken impression that hard drives typically overheat without a cooler.
The biggest load of crap is that you bought a seagate, presumably since they are the quietest option available, and any store-bought HD cooler is going to be ridiculously loud compared to the HD.
If you plug it in and think its getting too hot, try moving it where air is coming into the case, or intake air over it with a fan.
Edit: I own a 60gb barracuda ata V, and its suspended in elastic wire in a 5 1/4 bay. With nothing but the case airflow it is only warm to the touch.