Need Steam Help

[Fusion]

So on Steam I bought MW3 for £40.
I paused the "Call of duty MW3" download and just downloaded the "Call of Duty MW3 - Multiplayer".
After that both the downloads said "Ready to Play" and on the "Call of Duty MW3" download, which I click "start game" for the campaign, it crashes and says "error - iw5sp.exe has stopped working".
For the Multiplayer one, I find a game, and the map loads, then when the load bar is complete, it crashes and says "main/iw_12.iwd is different to the server". So I can't play a game either.
I really need help solving this. Please no stupid posts, I just need an answer Spent the whole weekend trying to get it to work

OS: Windows XP on VMWare on my iMac.

 

[Oxide]

Verify Game Intergrity cache, will fix it.

Also does your system match the requirments?

 

[Fusion]

I tried to vertify the game, then it updated and I can now join games. But the lagg is incredible. I can't play as the map barely loads.
If I change resolution there are text blocks and the brightness goes to the minimal setting.
I'll describe it better when I get home.
And I think my system does meet the requirements, but how do I check?