So...you want to slaughter a few cartoon characters of your own, do you?  It's actually not hard at all.
First, come up with an interesting idea for killing things (some of my favorite sources for ideas are the Spike & Mike's Sick and Twisted Animation collections).  Once you have a concept, yer ready to rip.  Open MS Paint (this comes with Windows... you can use a nicer program like Photoshop or something, but its not really necessary; Paint does fine for basic animations) and draw the first scene of your idea.  Save this picture as 001.bmp.  Change the picture slightly, like drawing a flipbook, and save this picture again, this time as 002.bmp.  Do this over and over and over and over until you've made an entire animation; you should have quite a few .bmp files now.  Basically, cartoons under 25 or so frames suck, as they turn out really choppy and short.  A good minimum is 40 or so.  To date, the longest animation i have is the dogman one, which is well over 100 frames.  Yes, it did take forever to draw, if you were wondering, but just think of people who draw bugs bunny cartoons and shit, they're tens of thousands of frames long.  Anyway, after you have a bunch of frames drawn, convert them  (in MS Paint you can click on FILE and then choose SAVE AS to convert; its easier than using a separate conversion program) to the file extension .gif
Now, get a GIF animation program like Gif Construction Set (my personal favorite); you can download the shareware version from sites like www.jumbo.com or www.download.com
Use the gif program to animate your files, and watch your creation come to life (and death)!
Cheers 
Mr. Slim