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Urm, you need to get your player model to be used with some specially tailored code: you can do this a number of ways, but its a _lot_ more involved than just adding a new mesh to the game. You can look on the wiki (I'd hope its there at least) or on the 'net, for the info needed to create your own PlayerPawn actor.
From there, you need to go through and change the fundemental physics of this pawn; not an easy process, but you can probally create a new state which handles this; not unlike say, swimming, and how it changes physics.... If this is your first code-project, you may want to try something simpler.
From there, spider physics in 436 is very odd, if I remember right: you can't walk from one poly to another, but rather if you land on a poly you stick to it, though your movement controls are a bit messed up. (stick, walk along, and fall off at the edge)
Though possible, I'd imagine, the basic unreal engine (esspecially 436) is not designed for AVP style wall walking; a lot of code would be needed to change this (I know, I've tried
) Neways, this is a pretty large code project, esspecially compared to importing a slightly tweaked player model into the game. I wish you luck, do some research, and don't fill the forum up with indistinct questions and single sentence answers.