each PC supports GigaByte speed. If each PC only has a 10/100 NIC, that's all you'll get. Since all switched PCs route through the router, the router must support GB also.
In short, all devices must support GB speeds to get what you want.
I am setting up a home network. I am currently using a wireless net work. I would like to hard wire 5 PCs using Cat 6. I am not presently concerned w/ internet speeds but I would like to have fast PC to PC speeds. Can I attach a Gigabyte switch to my router and get wired gigabyte speeds of transfer from PC to PC?