perl pattern matching

From: Niko (sanynn_at_hotmail.com)
Date: 08/31/04 

Date: 31 Aug 2004 07:57:56 -0700

Hi,

i need help replacing string in the middle of line like this :

var1:string:yyy:zzz:kkk.....:ggg

Need to replace the string.

I already know the value of var1, that help me to find the specific line in my file.

only left is to replace the string with a new string.

any idea ?

Thanks.