virtualbox.org

I enjoy tinkering with things and when i found this i got really excited because it potentially meant being able to toy with different OS's and find limits, bugs ect. without hurting my system. but i didn't want to dive right in without getting some information how safe it is. i have set up a virtual machine for XP and since i don't have an extra external hard drive to dedicate to a virtual machine i plan on wrecking i put it on my hard drive but i didn't share any files or folders. the only thing they share is a monitor and network access. but with them physically being saved on the same drive i am concerned. . . if my XP machine gets a virus will it infect my OSX? and if i wreck the machine so it doesn't run will i be able to clean up the mess it made on my macs drive?