Alan/Emack~
(this is going be a bit of a long post)
For the Creative sound card there is "mixer utility" that is avaialable via the creative site (last I checked it was in "beta" but it still does work corectly).
Mind you these are the steps I personally used, while on correspondance with a Creative technician via phone and email, to get my creative card to work correctly in Windows 7(Home Premium 64bit)
You go to creative and down load thier "mixer" program. In that program, there are selections for the diffrent ports to "activate" them. That will (or should ) in turn reflect in your Windows sound settings. It did for me. Its a little bit of tinkering but once all is said and done things should work correctly.
You can ALSO got to the Creative site and they have a "product detection" plug in that you can use to correctly identify your product to make sure you get the right software.
NOTE: you DO NOT have to have the "mixer" running constantly for the changes to "stick" . it is essentially a set and forget program.
You also MAY have to use Vista drivers if there are not Win 7 drivers avaialable. Those do work as well.
For the Memory compatability question you can try
www.crucial.com for compatable memory. There is a plugin they use whenyougo to the site that will scan your system and let you kwo what memeory is compatable with your system. They also have a "compatability gurantree". If you order from them (or acctually thier retailers as well such as Best Buy) if it doesnt work due to compatabilty or other defects they will replace it.
For the video, SOME systems will automatically switch off the onboard viseo when a independant card ( such as in your case the Nvidia) is put inthe system. If it DOESN't, which is sounds liek in your case, you have to lok throu the BIOS of the system to see if there is a selection to disable the onboard video. Or soemthign to that effect that has to do with onboard video.
However, that being said
TrainableMan is correct , check first that you have the most recent drivers installed for the NVidia. Also IF you have it available, check the card in a separate system to make sure it is working.
Hope the advice given helps. I know its a lot to read and take in all at once.
Keep us posted
LoneWolf