I installed 3com 3C905B-TX card in my computer which is running Red Hat 7 but it is not detecting the NIC. If the installation requires kernel compilation, how do I do that.

You don't need to necessarily recompile the kernel, best thing to do is read the ethernet howto at http://www.linuxdoc.org then if you have any questions or it still doesn't work, let us know after trying some of the stuff from the howto.