Inspiron 530s CPU Upgrade - Why some Dual Cores and not others?

Hi all

Inspiron 530s been chugging along nicely (albeit loudly), but has now been replaced, so decided to have a look inside, heatsink & fan felt loose so unscrewed it and lifted it straight off absolutely no resistance, so i am guessing cleaning the cpu and heatsink and putting thermal paste on would be a good idea.

While i had it open I thought i might as well upgrade the cpu chip as older dual core are going for around $10-15 here, (it currently has a 1.87? dual core in it), so i had a read of the forum to find what was possible

from the below post

http://en.community.dell.com/support-forums/desktop/f/3514/t/19372573

quote -- shesageordie

The Inspiron 530s has a FoxConn G33m02 motherboard made to Dell's specifications and will support the following Socket LGA 775 processors:

Intel Celeron processor 430                                        
Intel Celeron Processor 420 (1.6 GHz, 800 FSB)
Intel Pentium Dual-Core 2140 (1.6 GHz, 800 MHz FSB)
Intel Pentium Dual-Core 2160 (1.8 GHz, 800 MHz FSB)
Intel Pentium Dual-Core E5200(2.5 GHz, 800 MHz FSB)
Intel Core 2 Duo E4300 (1.8 GHz, 800 MHz FSB)
Intel Core 2 Duo E4400 (2.0 GHz, 800 MHz FSB)
Intel Core 2 Duo E6320 (1.86 GHz, 1066 MHz FSB)
Intel Core 2 Duo E6420 (2.13 GHz, 1066 MHz FSB)
Intel Core 2 Duo E6550 (2.33 GHz, 1333 MHz FSB)
Intel Core 2 Duo E6750 (2.66 GHz, 1333 MHz FSB)
Intel Core 2 Duo E7300 (2.66 GHz, 1066 MHz FSB) 
Intel Core 2 Duo E7400 (2.80 GHz, 1066 MHz FSB)
Wolfdale Core 2 Duo, E8400, 3.0GHz, 6MB, 1333FSB, 65W, E0 
Wolfdale Core 2 Duo, E8500, 3.16GHz, 6MB, 1333FSB, 65W, C0
Wolfdale Core 2 Duo E8500 (3.16 GHz, 1333 MHz FSB)
Wolfdale Dual Core Kit, E8600, 3.33GHz, 6MB, 1333FSB, 65W, E0

Also, the Intel Pentium E6500 2.93 GHz dual core processor.

 Prior to installing the processor you need to check that you have BIOS Version 1.0.15, or higher, when support for new Intel CPU's was added.

Note: Core 2 Quad processors are not supported by the Inspiron 530S [Slimline]

Bev.

Now theres my problem

Some of the cheap used processors available locally seem to not match those numbers (and they seem to be a bit cheape than the ones that do match up)

for instance E6850, E7200, E8200 what about these processors prevents them working?

 And as a side note will I need to upgrade the heatsink and fan, if I get a different processor?