Rounding (sharo) edges

I know, i know, question is sooo stupid and for someone who is working in photoshop CS3 4 days not 4 months. But for life of me i cant remember where to go (i think filter) and what to click to have option to round edges. I saw that once when i was reading some tutorial but forgot it tomorrow.

Can someone help me?

Make a rectangle with the rectangular marque tool. Then Select-Modify-Smooth, enter a number for the pixels, change the pixel count as necessary to get the results you want.