1.) Some would note that ideally your RAM would always be near 100% usage. The reason is that the alternative to RAM usage is utilizing your hard drive for extra space, which is extremely slow in comparison. The more RAM Windows uses instead of hard drive space, the better. You can check Task manager to see how much "virtual memory" (paging file/hard drive space) is actually being used.
2.) Depending on what you are doing, there may be no need to worry. If, for instance, 66% is being used for the most memory-intensive tasks you performed, you're good to go.
3.) If you have integrated graphics as opposed to a stand-alone graphics card you can bump up your available RAM by 128MB-256B by purchasing a graphics card, which would also greatly improve your graphical performance. Why? Integrated graphics use system RAM as their source of memory (they have none of their own), and they are far slower in an effort to reduce cost.
Aside from that, 1GB is the minimum for 'premium' Vista performance, so, while acceptable, you would ideally want 1.5GB+ for multimedia and multitasking activities.
I recently bought Vista and the ram gauge on the the gadget bar says 66 percent i currently have 1GB and i think i might need another, any suggestions.