I leave my main computer on all of the time, it's only shut off when I go away for more than one or two days. It does reduce the wear and tear on the buttons and the hard drive. You don't have to disconnect your modem when you turn it off, it's not possible for someone to get into your system while your computer is off and really with todays technology people don't really hack into regular joe's computer to take stuff because most people don't have a lot of vital info on their computer. They'd need your IP address and your firewall would need to be off, if you don't tinker with your XP settings than it is usually on.
I say leave it running and only reboot once and a while if it's sluggish or run the various clean up programs that come with XP, if that's what you're running.
"Until one has loved an animal, a part of ones soul remains unawakened."
Proud Parent of:
Kip - Female, DSH Cat
Moxy - Female, Lab Cross
Dagan - Male, Husky/Malamute Cross