Hi, if i want to upgrade my 2.4.x kernel in slack to a 2.6.x...is that the same thing as compiling a kernel?

Well, you can either compile it or use the one precompiled from the Slackware's cds. Read the file testing/packages/linux-2.6.7/README.initrd in the cds if you want to upgrade using the precompiled one.

Can you compile it to be 2.6.x?

Kernel 2.4.x and 2.6.x are two different source codes. If you going to compile your own kernel I just you take a look at some of the stickies (there are many) on kernel compiling, as well check out kernel.org, there you will find the source code to all different kernel versions.

If you just want to upgrade from 2.4 to 2.6 I suggest you use the kernel already compiled for you on the slackware cds (can't remember which one). It will be in a folder called /testing. You need to mount the cd then find that folder, after which you can do upgradepkg kernel-2.6.7 or whatever.