Yes, stay with the 2700. I remember those days and switching to 3200 myself did nothing noticeable. Like Antas said, get another 1G for a total of 2G's. That is the best move for your current system.
How many memory slots do you have? If you have 4, you should be able to install 2 more 512mb sticks or if 1G is cheaper install in this order:
512 - 1G 512 - Empty
You want to match the offsetting slots for most motherboards. DDR is very expensive these days and almost warrants building a new system IMO. I actually recommend building a new system if you are totally disatisfied with your system. If you just need a little boost to make you happy you need to answer how you use your system. Gaming or programs?
If gaming, get a better video card. If program performance is what you need that could be a CPU/Memory issue and adding another 1G may not be enough if the CPU is maxing out.
If you have the money go with a new system build. If not, then do the upgrades based on what I said...