Not true. You can scale the ram to what you want it to be, its not needed to be a multiple of two. There's 1GB sticks as well as 3GB sticks (old windows XP days could only support 3GB max, so people thought it was a good idea to make them)
As well, use SSD's, hard drives are the largest bottleneck, most people think they're PC's are slow because the CPU or RAM is not fast/large enough, this is wrong, most of the times (unless you use a windows 95 w/ pentium III box) its the hard drive that is not able to deliver data fast enough to the processor, and therefore not allowing the PC to operate at full capacity, this is also called I/O Wait.
I have a MacBook that boots in 4 seconds from cold to the desktop, way to go with the SSD's :)