What's the real difference between chips?

[judder]

I'm not a computer whizz so please be gentle. I am looking to learn and build myself a computer (preferably with a small form factor). My research seems to suggest that Intel chips are always more expensive (sometimes considerably so) than their AMD equivalents. Are they worth the extra money?

Is there really much difference (in every day use i.e. not for serious gaming) between a Celeron, Pentium and Core-Duo (or whatever they are called) and all their subcategories?

Finally, what chip should I get (I realise this could spark as many different answers as people who take the time to offer an answer), given that the computer will be used for writing documents, spreadsheets, databases, internat and occasionally running some Fortran programs under a Linux partition?

Thanks.

 

[judder]

Thanks for that. Though I have a 2 year old laptop running a 2.4 GHz Celeron with 512 Mb RAM. Would these Core 2 Duo chips result in a slower machine than my laptop?