Either the vmlinuz or initrd could have numbers after them. It's just a disk file. Most programs are files on your disks - kernels are just special in that they want to be the first program to run on your machine so they can control other programs.
Every operating system has one.
If you did not understand the previous two sentences, don't worry. Get your distribution's boot diskette, grab the vmlinuz file off the disk, or grab another kernel off the net. As long as it supports your hardware, it's fine. This could scramble your hard disks though, so back everything up before trying it.