what about pentium 4?
is it true that pentium d is the best, pentium 4 is second and then is celeron d?
yeah, but i will likely pay more for pentum e and motherboard then just for pentium d/ p4 / celeron d...
To an extent. There were some higher-end P4's (wicked fast clock speed and HT) that would run circles around some of the D-series, namely the 8xx's. Once the 9xx's were introduced with a different architecture, really the only P4's you could compare them with were the 3.6 and above with HT. I had a D940 for a long time and loved it. It handled everything I threw at it with relative ease, stayed cool, and was extremely reliable. OC'd well, too, I recall
Like 2048 mentioned, Celeron D's are single core, not dual. Lots of people see the 'D' designation and automatically assume it's multi-core. They're actually good, reliable CPU's for certain builds. In the company of a P4 and D-series, though, just remove it from consideration.
Anyway, if you're going to get a D-series, definitely go with a 9xx, preferably a 940. Stay away from the 8xx's. However, if you have a chance to grab one of the nicer P4's (see above), that would work, too. Just make sure the P4 you get is the correct Socket type for your MoBo.