Daratum,
Dell Inspiron 530 manual >
ftp://ftp.dell.com/Manuals/all-products/esuprt_desktop/esuprt_inspiron_desktop/inspiron-530_owner%27s%20manual_en-us.pdf
I could find only one Inspiron 530 on Passmark benchmarks with the 0G679R motherboards and that had a core2 Duo, but the manual says that Quad core Socket 775 CPU's may be used. Using the same Socket 775, 1066FSB, and 65nm lithography, the fastest CPU for your Dell Inspiron (see page 179 owner's manual) may be the 4-core, Core 2 Quad QX 6800 @ 2.93GHz / 8MB cache. This would be a dramatic increase in total computing power, but in some single threaded and 2D applications- which many are, the difference in some applications between 2- core 2.8 and quad core 2. 93GHz may not be dramatic enough to warrant the cost. The QX 6800 is also quite expensive >
http://www.ebay.com/sch/i.html?_sop=15&_sacat=0&_from=R40&_nkw=Core2+Quad+QX6800&LH_Complete=1&rt=nc
> these are often about $120. Note > E7400= 65W, QX6800=130W
If the motherboard will work with the quad cores in that line, a core2 Quad Q6700 @ 2.66GHz for about $45-50 or the Q6600 @2.4 for $30-35 are good choices. Q6600= 105W , so for any change to quad core, you will want to upgrade the cooling. The 530 uses a fan/heatsink combination and as the system were supplied new with quad core CPUs, there must be a model number for that use.
In Passmark benchmarks, the system ratings for an Inspiron 530 / Q6600 / GTS 450 system is a respectable
1443 with 2D / 3D scores of 371 / 1661 while an Inspiron 530 / Core2 4500 (2.2GHz) / 9500 GT, rated
788 with 2D / 3D of 325 / 296.
Of course, a lot of the difference in these two systems' 3D performance is due to the video card, but to some degree it is also the CPU architecture unlocking the GPU power. So, if you upgrade the CPU, consider also a reasonable video card and the system could perform quite well. Look for deals such as >
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127703
-which is a very competent GTX 650 which after a rebate is $70. If your friend's parents only write letters and browse the Intertubes, you can buy a GeForce 630 for $60, or 610 for $40. There are also good Radeons in those price ranges and Radeons often seem to perform a bit better at the same price as NVIDIA.
You
may be able to use 8GB RAM- The manual mentions the "530a / 530c" as using 8GB. You might want to confirm the ability of these particular 530's to do this before buying copies of 64-bit Windows. An updated BIOS
may - no guarantees- may allow the use of 8GB RAM. I worked on a Dell Precision 390 (from 2005) recently and the BIOS upgrade made 8GB possible. I would say though that if you can't use 8GB RAM, you may as well stay with the 32-bit Windows and only add to have 4GB. Note> the manual says the 530 uses DDR2 667 / 800 and in your list you call it "253".
It appears these systems have some good potential.
Cheers,
BambiBoom