I've a Sony PCG-Z505S. Would I be able to use a new motherboard, processor, hard drive to get it up to today's standard? The magnesium case and screen resolution are great but it's slow and running Windows 98.
I doubt any modern motherboard will match up with the output ports in a older case like the PCG-Z505S. And that's just the first of many problems you'd have to deal with.
In most current 12" laptops you'd get a 1280x800 or 1366x768 LCD panel.
For something like this you'd want to ask in the Sony forums and hope to find someone whose already done that type of thing to save you a lot of the work figuring things out.