I have Dell XPS Dimension Gen2 3.0Ghz processor
Package Socket 478mPGA
Chipset intel i875P
is it possible to get better processor and witch one
No not really, I mean not anything worth while. According to Dell this is what it says
Processor typ: Intel® Pentium® 4 that runs at 2.4, 2.6, 2.8, 3.0, 3.2, and 3.4 GHz
If you have a Pentium 4 running at 3.0 Ghz you can upgrade to a Pentium 4 at 3.2 or 3.4 Ghz but the performance increase will be next to nothing and it's so old it isn't worth it. I would just get a new computer.