Everything you need to know about that board is here

If you look at CPU support, you can go up to 3700 with an Athlon. Athlon's are generally faster than Semprons.

You can go up to 2Gb RAM. Stick with DDR400 (pc3200) RAM.

I'd say it might be worth upgrading if it fits your budget. You can get 2GB RAM here at a good price, and an AMD 3700 here

Don't forget, the links I've posted are the maximum, so look for lower end CPUs if you want to reduce your cost. The RAM is always worth going for the max if possible.