[CentOS] Where is the kernel source code???

I have centOS 4 installed on my machine but some how it does not 
support my TV capture card (bt878) in the kernel, so i want to 
recompile the kernel to add support for my device. However, i cant find 
centOS 4  kernel source code. I have read some messages in the mailing 
list and someone said that i just need to
yum install kernel-sourcecode
to get the source code, i did it but i yum reported that there is no 
package matched. Please help
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