Do Not get that nvidia card!!! Unless you are planning to buy a 9800 Retail card after you buy, upgrading to the Radeon 9600 is the best upgrade possible for that machine. The nvidia card is rock bottom and you will see much better performance from the 9600!
Also, how big is your VGA monitor? Is it big enough that getting an LCD will just be something "cool" instead of something that you need? If that is the case, I would suggest getting the RAM instead. The RAM will increase overall speed, especially on such a fast machine.
I find that a VGA monitor can be very nice, depending how sharp a picture you need. In my case, my Trinitron is visibly more blurry than my LCD, but I still use it more because its bigger and is more scalable for different resolutions (LCDs become horribly blurry at anything but the recommended resolution).