external hard drives and storage

i have a new seagate internal 160gb sata drive. i was thinking of getting an enclosure to make it an external drive. personally i do not trust any storage in the case itself since it is always connected. even though it is a totally seperate drive from the main hd, it can stil get corrupted via spam spyware and viruses since it is constantly connected. so i wanted to make this hd a removable storage hd. i know i would have to buy those sata pci cards to connect them as well as a hd enclosure. does the hd enclosure come with a power plug? how exactly do they work with external enclosures? is there anything you guys recommend or should i just buy a regular external eg: western digital or seagate or other that connect via usb or firewire and save time?
thanks