of the old RAM? If your processor was the Celeron, faster RAM isn't going to help. At 250 megs, you were a bit thin anyway so the 1 gig is fine. I'd say if you pulled a 400mh module, you'd want to replace it with one of the same speed and not slower.
Recently I bought a 1 GB DDR ram as a upgrade from 256 MB one that I presently use. However later I noticed that the 1 GB ram is 333 and my motherboard supports both 333 and 400 rams. So should I go for the 400 one or is there no big deal in using the 400 one instead of 333? Is there a difference worth noticing? My motherboard is intel D101GGc.