same problem here,this is what i found to solve the problem
Method 1: Resolve Issues with Soundcard Driver
Iw3mp.exe error is known to occur due to problems with sound card drivers. One method that is known to resolve the issue is to uninstall the sound card drivers for realtek and other similar cards and install the default driver on the PC.
You may use the following method to uninstall sound card:
Open Start menu, select Run, type sysdm.cpl and then press Enter to display the System Properties dialog box.
On the Hardware tab, Device Manager.
In the Device Manager window, expand Sound, video, and game controllers.
Right-click the sound card driver and then select Uninstall.
After uninstalling, it is recommended that you use a good registry tool, such asRegGenie to clean your registry and remove any left behind entries. After removing the sound card, install the default sound card drivers on your PC. When you do this, note the make and model of your sound card. You may need this information later on.
Method 2: Install Required Updates
You may need to update the following:
Install Call of Duty 4, patch 1.5. Before installing, ensure that you already have patch 1.4 installed, otherwise you may encounter problems.
If you are running the game on a secondary partition, you may have to download the latest BIOS updates from your motherboard manufacturer and follow the other applicable solutions posted.
On Windows Vista Dell computer with Sigmatel onboard sound cards, you may be able to resolve the error by installing latest Windows Vista update and updating the Dell drivers. To update drivers of your PC easily, you may choose to use a reliable driver scanner tool such as Driver Detective to the task automatically for you.
Method 3: Use Headphones When the Game is Running
You may do one of the following:
· Change default audio device to headphones and then play the game.
Plug in a microphone or headphones into the microphone/headphone jack to play the game.
Method 4: Enable Stereo Mix if you have Realtek sound card drivers on Windows Vista computer.
Open Control Panel.
Select Hardware and Sound.
Select Sound and then display the Recording tab in the Sound dialog box.
Right-click in the window and select the Show Disabled Devices option.
Enable Stereo Mix.
Click OK and exit
hope this work ,cya on battlefield