Can anyone point me at a site that can explain the difference between the various chipsets, or perhaps tell me what will be the best, most future proof option that will make the most of the cpu?
Intel has two main chipsets in your budget range, mainstream and enthusiast.
For Core 2 Duo the first generation was P965 (mainstream), which was accompanied by 975X (enthusiast), 975X was not designed to be used with Core 2 but with dual cores it performed very well (and still does).
The next generation was P35 (mainstream) and was followed (eventually...) by X38 (enthusiast).
X48 is not a replacement for X38 per sae, it is the same chip but comes with official Intel certified 1600 FSB CPU support.
Lastly P45 is the mainstream replacement of P35 and is probably the last LGA775 chipset. It is most remarkable for enabling PCI-Express 2.0 support with 2, 8X / 8X PCI-Express 2.0 slots.
Intel 975X (with ICH7R):
Official 667 Mhz DDR2 (Unofficial 800 Mhz DDR2)
PCI-Express 1.0a & 1.1
8X / 8X Crossfire
native IDE, SATA
Intel P965 (with ICH8)
Official 800 Mhz DDR2 (2 DIMMs only)
PCI-Express 1.1
16X / 4X Crossfire
SATA (native IDE removed from the southbridge)
Intel P35 (with ICH9)
Official 45nm CPU support
Official DDR3 and DDR2 800 with 4 DIMMs
PCI-Express 1.1
16X / 4X Crossfire
SATA
Intel X38 (with ICH9)
Official DDR3 & 1333 FSB
PCI-Express 2.0 (Northbridge) & 1.1 (Southbridge)
PCI-E 2.0 16X / PCI-E 2.0 16X Crossfire (May have a 3rd PCI-E 1.1 slot running at 4X)
SATA
Intel X48 (with ICH9)
Official DDR3 & 1600 FSB
PCI-Express 2.0 (Northbridge) and 1.1 (Southbridge)
PCI-E 2.0 16X / PCI-E 2.0 16X Crossfire (May have a 3rd PCI-E 1.1 slot running at 4X)
SATA
Intel P45 (with ICH10)
PCI-Express 2.0
PCI-E 2.0 8X / PCI-E 2.0 8X Crossfire
SATA
Notes:
P965 overclocked very well for the time but didn't do quite so well with quads, P35 was and (still is) exceptional for overclocking. P45 clocks well and is basically a die shrink of P35 with PCI-Express 2.0 and improved Crossfire bandwidth.
Intel 975X is an excellent, mature chipset but overclocks poorly with Quads and like P965 doesn't have official support for 45nm CPUs. I would avoid boards based on 975X and P965.