Wanted C#/XNA 2D physicist!

Amazed yet?
It's a 2D platformer/action game in the works, programmed in C#/XNA!
So far it features readable signs, turrets, shooting, sounds and a 32-bit color palette!

Of course you may play it! Here: http://filesmelt.com/dl/greatest_game_in_world_tribute.zip

So yeah, I'm working on this game/engine and pretty much everything is going great, but I'm having massive issues with physics. This is actually the first time I've pulled off semi-working collision response.

I really doubt I'm able to make it good on my own, so it would be awesome if someone could fix it for me as a favor.
Here's the physics code: http://pastebin.com/Ykq1HWcn

If you're up for it, I'll be happy to hear from you.