I'm using Windows XP Professional SP2 on a single core AMD64 processor, and I've got two instances of MsMpEng.exe starting up when I start up and log in. They use 64MB and 32MB of ram and 140MB and 80MB of virtual memory, and fluctuate around 80% CPU usage for about 5 minutes at start up. They are (I read) associated with Windows Defender, but I'm concerned about:

• There's two of them, everything I read generally has only one reported.
• They might be scanning each other, and I want that to stop.
• They might be getting scanned by avgrsx.exe (AVG Free 8) (uses about 16Mb v ram)
• They might also be scanning moe.exe (assosciated with ms live mesh, which I'm considering getting rid of)
• Lastly I have Microsoft Security Essentials. I don't know the process name associated there.

The main concern of mine (apart from the double instances) is that these are all trying to prioritize scanning each other at once except maybe moe.exe. This might seem legitimate but is likely a useless drain on resources.

Have I made a mistake in having all of these installed, or is there a way to inform them not to do whatever they're doing that's taking about 5+ minutes at start up? [I also have Google Desktop, but I'm keeping that.]

Comment if none of this makes sense to you.