Assuming dell bios will recognize a core2quad cpu, the difference will be minimal.
You have a 10 year old computer that is bassicaly 10% of the performance of what modern software expects.
Getting a better cpu might up to 15%. While 15 is 50% more then 10, it is still grossly insuficient and thus a waste of money/effort (even more so due to risking damaging the pins/socket or poor thermal paste application overheating the cpu).
Thus money will be better served just saving for something modern.
If you had a 5 year old PC with say in i3 2xxx cpu then sure upgrading will be worthwhile, but in your case it wont.