2^32 = 4,294,967,296. 4,294,967,296 / 1,024^2 = 4,096 bytes

(Incidentally, 64-bit has a theoretical limit of 16TB of RAM

)
You'll need to check with your system specs as to what power the PSU is. New cards (the 9xxx series Nvidia, with the 8800GTX not far behind) need much more power than a 7100. I'm not sure on Acer, but I know that Dell and HP use odd PSUs that are a headwrecker to source and replace at times.