I've been reading a bit about the i7 chipset and wondered about this x58 architecture. What does that mean exactly? How different is it from x86?
You're mixing two things up... x58 is a chipset used on the motherboards for i7 processors, x86 is the family of Intel processors that i7 is still a part of.
To kind-of answer your question, i7 is still part of the natural progression of Intel processors, latest and greatest... and if you want to use it you will likely be using an x58-based motherboard to run it.
x86 is an instruction set applying to the full line of Intel chipsets. The x58 is a new chipset.
Wikipedia appears to have the scoop on x58 itself.
The QuickPath architecture differs considerably from earlier Intel architectures, and is much closer to AMD's HyperTransport architecture. Except for the lack of a memory interface, the X58 is similar to the traditional northbridge: it communicates with the processor(s) via the high speed QuickPath Interconnect, it communicates with the southbridge via DMI, and it communicates with high speed peripherals via PCI-E.