3Gb will be the size of the RAM, not the storage space for files & programs - I'd expect that to be 100Gb or more. The processor speed will be given in Ghz (gigahertz) - 2.0Ghz or more is common these days.
But the speed of the computer depends on both the processor speed and the amount of RAM - the higher the processor speed, the more instructions the computer can process per second, RAM is the temporary storage place for your computers information. If all your usable memory gets filled up, the computer will then start storing temporary data on to your hard drive in something called a swap file - and retrieving data from there is slower than from RAM.
3Gb is quite good though, even for running Vista - my laptop's OK even with only 2Gb RAM & 1.67 Ghz processor, but then I don't do a lot of intensive games.