Plado - Welcome to the Windows 7 Forums website!
To be honest, you'll be fine with 4GB of RAM to start with. I ran with 4GB of RAM for about a year and then added 2GB more. I did this mostly to assuage my ego, it had nothing to do with any specific need that's for sure.
Even when I'm doing very heavy video rendering or conversions I use no more than about 2.8 GB of RAM.
Have you considered building your own system? It's very easy and doesn't take too long at all. Just a thought, besides why strap yourself to a neutered motherboard and PSU that the majority of the major PC makers supply.