Since I had to shoot many of my photos in high ISO speed, my photographs have now turned grainy. Does anyone have any techniques to reduce noise using Photoshop. Thanks in advance.
You should let us know if you shoot digital or film. I am assuming digital, but your use of the term "grain" implies film.
Noise reduction is well covered in the many essays and threads on this website. Do some searching around.
There are two dominant Noise Processing addins for Photoshop: Noise Ninja and Neat Image. In addition, Photoshop CS2 now has built-in noise reduction capability.