Celeron is not better than a Pentium 4. Celeron is Intel's cheapest processor which is why your machine didn't cost that much. If you're just doing regular everyday tasks on your machine - surfing the Internet, email, word processing, etc. the difference between the processors won't matter to you.
As for eMachines, I stay away from them as a rule. I've had family and friends who bought them in the States (there's always a ton of them at Best Buy with lots of rebates) and all had huge headaches and extremely poor customer service from eMachines when they tried to get them fixed while under warranty.