Suspension, Brakes, Tires & Wheels - RIM Size for 2005 Civic SE

hey all:

I just bought a 2005 Civic SE and would like to put some nicer rims and tires. What size rims and tires are best suited for this car? When rim sites ask for bolt pattern what is the example 4 X 100 mean (specifically the 100)? Also rim displacement.The car is in great shape but it is a comuter carthat I just want to make it a bit nicer. Any help would be appreciated.

Thanks,

Gerry