Your situation reminds corresponds to mine. Until my last conquest, I had DDR memory but no machine to use it in.
An Athlon 1000 isn't too bad depending on what is done with it. Also with DDR it may support something faster, up to an AthlonXP 3200+ depending on the chipset on the motherboard. If not that fast then most likely up to a 2600 with 266mhz bus speed.