According to one posting, if your system was sold before May 6, 2002 it uses 400 fsb cpus. After that date, 533 fsb p4's should work. The 3.06 you have should be easy to recover your money on if you list it on craigslist. Starmicro has some 400 and 533 cpus fairly cheap.
Yes, the system was shipped in November 2001 and has the 400MHz FSB. So I guess I need to stick to the 400 FSB processors? I have a 2.0 GHz 400 FSB processor and the Dell documentation for the 8200 shows a 2.4 GHz processor as the fastest 400 MHz CPU for the system.
I recently found some affordable RDRAM and upgraded the memory from 512 MB of 45ns modules to 2 GB of 40ns modules, which improved the system performance a lot. I'm wondering how much difference upgrading to a 2.4 GHz CPU will make in any case.
Thanks for your advice.
Update, 2/22/2010: I checked with Starmicro and found a very inexpensive P4 2.8 MHz 400FSB processor that should work. I decided to give it a try and ordered one.