The problem with the older celly's was that their performance was cripples by their little amount of Cache. With the celly D, this chanced, and those Celly D's are actually quite capable chips.
The best way is always to compare specs, and for a CPU you should look at the following:
Architecture: in this case, both Netburst. However, the 1.7GHz P4 is a Willamette core, which is the oldest P4 core. The Celeron D is either a Prescott or a Cedar Mill (is it the 355 or 356?), which is a much later version of the Netburst P4 architecture. Winner: Celly D
Cache: Either same cache (if you have the 355) or double the cache for the Celly (if you have the 356). Tie, or winner: Celly D
FSB: 533MHz v. 400MHz. Winner: Celly D
Socket: LGA775 v. 478. Winner: Celly D (support for DDR2, and just a newer technology)
Support: Celly D supports 64-bit, the P4 doesn't
Finally, clockspeed: since the Celly D is already ahead in almost every aspect, the nearly double clockspeed pushes it way ahead.
TnB= Gir: These chips are about as dissimilar as two chips can get within the same architecture (except Pentium D Dual Core). The Celeron D 3.33GHz he's talking about is either a 90mm or a 65nm chip, while the P4 1.7GHz is a 180nm chip... plus, quite a few differences in technology (64-bit most importantly).