Urgent!! finding a string in a file

I got a file here,and there are a number of data. What I need to do is that I will go through the file, and finding the letter "T" in the file. Then I save the letter and all related data into another new file. My question is how to go through the file and find the letter"T" in the file. And how to put the letter and the related data into the new file??
Anyone can help me out, I will very appreciated.

read a chunk of the file into memeory and scan for a 'T'
then, you need of course to know what the SIZE of the related data is already, so read it from memory and save it in a the new file

sally

Can you explain more detail of the content of your file? Maybe someone can give you more hints.