I heard that the best way to determine system configuration is to look at the minimum requirements of the operating system and all the software you plan to run on it and at least Double it......
Not really. It is more what version of OS you are running and what apps you are running too. Basically with XP you want a MINIMUM of 1 gig of memory. With Vista do not even try to leave the gate with less than 2 gigs. Basically there is nothing wrong with Vista other than is need a good bit of ram and decent/compliant hardware. It got a bad rap because it was sold on system not properly configured for it hardware wise. Win7 is nothing more than a tweak of Vista and with a new UI (user interface) While XP will not gain performance with more than 2 gig, Vista will and so will Win7. Now with 32 bit Vista or Win7 there is no reason to ever install more than 3 gig because 32 bit OS can only see/use 3.2 gig max at one time. With 64 bit Vista 4 gig is minimum and 6 or more better still. With Win7 64 bit, 4 gig will run pretty decent for most uses. On a limited budget, ram is more important that CPU speed. Do not scrimp on ram for more CPU.