In which case would it be better to have a Celeron 430 processor than a Pentium Dual Core processor ? And in which case would one prefer to have a Pentium Dual Core processor ?

The Celeron 430 would be much better if you prefer to keep some of the money you would spend on a Core 2 Duo. In all other cases, the Core 2 Duo would be better

Prices don't differ a lot between the Celeron and Pentium Dual Core (E2140-E2180). Dual Core comes as cheap as THB 2,100 ....

1 - Decide what is your main use of your computer ...

2 - Look for benchmarks ......

Both the Celeron 430 or the Pentium Dual Core are processors which I can recommend. The cheapest Core2 Duo runs circles around the fastest Pentium Dual Core, also the Core2 Duo uses much less power and produces much less heat. Making it very good for overclocking without risking damaging you processor.

A celeron would be better in case if you want to use the Computer as a Web-Server for Webpages, E-Mail Server or something like that. For this you don't need high performance but stability and a Celeron is very good for that. I Run my Webserver's on Celeron or AMD Sempron only!

For normal daily computer works I would go with Dual Core!

Sorry not forget that only the Intel Core2 Duo and Core2 Quatro are faster then AMD.

AMD processors in the same price class as Celeron and Pentium Dual Core are faster and mostly cheaper....

If your main objective is to create documents, or use the Net, and have no need for 3D games, Photoshop, programs which require intensive math calculations, or other graphic-intensive applications, you will save money by getting a Celeron. A Celeron-powered computer can still perform all of these functions, just a bit slower. And speed is not an issue when word-processing or doing spreadsheets, nor will it affect the performance of your Internet access.