First thing I'd do, is update my urpmi sources - because some of the mdk packages aren't the very latest (and they're working on 9.2 stuff anyway) and as you can see from your post - there is a version conflict - often one of the easiest ways to correct this would be to uninstall SDL1.2-1.2.5-5mdk and although I haven't checked, you could well find the 1.2.6-1 has been packaged by either the plf or texstar (this is certainly the case for xmms).
So, google to the plf site, look down the page and locate the link to "easy urpmi". follow that link and then read the page instructions - select a mirror for everything i.e. don't skip any sections (and the mirrors closest to your location should be the fastest - though not necessarily) don't forget mirror sources for texstar at the bottom.
The output of you info is then displayed in the large panel at the bottom, you have to cut and paste this into a terminal/konsole (I didn't have to even enter it, it just started after the cut and paste - though I had to enter when it seemed to stop). Anyway, once you are back to the shell prompt, you can close the shell/terminal/konsole/whatever, and go into mandrake control centre and open the software manager. You would need to got to the "rpmdrake -" bit and dig through it to find the SDL1.2.-1.2.5-5mdk package and uninstall it. Then got to the "rpmdrake+" bit and I'd probably select the list packages alphabetically, run down the list and find the most up to date version of it (presuming SDL1.2.6-1) and if it needs anyother libs and stuff for dependencies it should select them as well (don't worry if it's not mdk, but plf or tex - theyre the packagers), then just hit install and off you go.
Dont forget, some of these packages are quite large, so if you are on dialup, it could take quite a while to down load (if it's not on the mandrake discs).