Personally, I would wait until summer. Let all the chipsets get on the market and the first wave of revisions to hit the streets. The KT133a chipset doesn't have a really big performance increase over your KT133 chipset now. It is more or less the ability to run the processor at 133 MHz instead of 100.
There really isn't any DDR boards available that are tweaked out and ready to go yet. Give them a few more weeks and the reviews will be abundant to read through. Some are appearing, but there will be a couple chipsets to choose from: AMD, Via, and Ali.
Just my .02