You'll have to find out from Dell if a Quad Core is supported and a power supply upgrade will be required if you only have a 160W unit. If you consider replacing the power supply, motherboard and CPU, then you may as well get a motherboard that supports DDR3 memory.
Two questions for you, as my computer proficiency is only slightly above the average user.
First, how would I go about ensuring everything is compatible with upgrading to a new motherboard/processor ( The example you provided me, unless you did the legwork for me already )
Second, would the example you provided give a better boost to processor power than a quad core at lower speeds, especially when a quad core could have each core dedicated to a instance of the game in question?
Sorry for my lack of knowledge, Im sure it can be a pain answering what may seem like simple questions.
With my suggestion you have a modern CPU and motherboard. DDR3 is what is ram std today and would have been an issue if you had ddr2 ram and I am presuming that since you have DDR3 your disk drives are SATA which is now the std not IDE which is not supported on most new motherboards. Another issue is your Win licenses is tied to your Dell and they might not allow you to reuse it.
The Q8300 is three generations old now but there will not be any OS (win) issues just with the CPU upgrade if supported.