Please Help! MotherBoard VIA K8T800 or Nvidia Nforce 3 250

I am currently running:

AMD Athlon 64 3200+ CPU
Asus K8N-E MainBoard
3GBs G.skill Ram PC 400
2 SATA Hard Drives
ATI HD3850 512MB 8x Graphics Card
Audigy 2 sound card

I was curious is there a huge differnce between the two? I love gaming I have some how kept on the curve with a 754 processor and 8x agp graphics card playing the latest games. FarCry 2, Fear 2, and so on. I want to know would it be wise to switch to a motherboard i got from a friend. (MSI K8T Neo FSR 6702) I want to know if it is as good as my asus as well I need to know if it is true that once you place PC 400 DDR ram in it will only acount for 2gigs of my 3.

Questions:
Is there a difference between Nvidia Nforce 3 and Via K8T800?
Is it wise to switch to the MSI board or Should I keep using the Asus?
As well does the MSI only support 2GB of DDR400?

Side question, When I placed my MP3 player cable into the USB port it made my computer one time shutoff. Since then my USB ports will not work and wondering beside the fact of having to buy a USB Card. Could that affect anything else on the board branding me lucky that it didn't frag it entirerly. Also I noticed that when I plug something it it detects it just doesn't process whatever is plugged in.