I am looking for a trainer that will work on the Steam version of MDK. One that will grant invulnerability/no damage for sure, infinite ammo would also be nice.

Does such a thing exist?

I have no idea if such thing exist, but you can try with cheats.

Type "givemealliwant" and then :

dum -- dummy decoy
wmi -- world's most interesting bomb
nuk -- world's smallest nuclear explosion
thu -- thumper
twi -- tornado
tii -- tornado
hbo -- hand grenade
bon -- bones airstrike
gat -- super chain gun
hom -- homing bullets
sgr -- sniper grenade
hgr -- homing sniper grenade
lgr -- mortar

I found this page:
http://www.mobygames.com/game/mdk/hints/hintId,17123/

It has the cheats you listed and a few others.

One cheat it has is:
iwillnotbestopped -- Kurt cannot be killed by conventional means

that's the core cheat I want! Sadly, it doesn't seem to work for me when I try to type it in.

Any ideas? (I would simply rely on makemefull or healme, but you can't use those more than once every so often.)

Thanks!

With "givemealliwant" and then "gat" you don't even need health, because aliens will have no chance against you

You can try with this one, but I'm not sure if it will work with steam version.

http://hectichq.com/downloads/MDKCHEAT.rar

I'll try that trainer. Sadly, my mad skills aren't great. Plus I love in these games to be invulnerable, so I can if I choose ignore the baddies and scope out the level/arena.

If that trainer does the trick, that will be awesome, but if not, I may just skip MDK.

Thanks for the link.

To be honest MDK is very easy and short (unfortunately) game. You should have no problems, even if this is your first time with MDK.